The smallest elements to consider when looking at English grammar are individual words, sometimes called parts of speech. These combine into phrases and clauses which in turn combine to become sentences. Sentences can be of different types with different functions.

Types of Words (Parts of Speech)

Knowing the names for the function of words in sentences is mainly useful to help you discuss your writing. (For example, someone might say to you, "Try to use more adjectives," or, "It would help if you made your verbs more precise.") SO use the explanations which follow as references just in case you need them.

The first thing to know is that words become parts of speech only when they are used in sentences. The part of speech they become is determined by their use in the sentence.

Content Words

These carry most of the meaning in the sentence.

Nouns

Nouns are names and identifiers of people, places, things and ideas. They become nouns when they are used in sentences as doers or receivers of actions:
The player popped her bubblegum.
(Both words in bold type are nouns - one doing the action, the other receiving it.)

Proper Nouns

The names of specific people, places, companies and institutions are capitalized. They are also known as proper nouns.

Singular and Plural Nouns

Nouns can refer to one person, place, thing or idea, in which case they are singular (a desk, a box, the computer, a girl).

They can refer to more than one; in which case they are plural and their endings change to signal this, in most cases by adding the letters 's', or 'es' (the desks, some boxes, many computers, fourteen girls).

Pronouns

Pronouns are words used in place of nouns, often to avoid repeating nouns.
Sarah loves spinach. She really likes it.

The pronoun "she" replaces the noun "Sarah," and the pronoun "it" replaces "spinach."

A cow is just a machine that makes grass fit for us to eat.
The pronoun "that" refers to the noun "machine" and the pronoun "us" replaces the noun "people."

Always make sure your reader knows what noun your pronoun is replacing. Here's an example where it is not clear. We are not sure who the "she" is in the second sentence.
Sally has a cat. She is very beautiful.
Depending on the meaning intended, this would be better written
Sally, who is very beautiful, has a cat. Or Sally has a cat that is very beautiful.

Pronouns, like the nouns they replace, can be subjects or objects in a sentence. Unlike nouns, some pronouns change their form when they are used as objects.
Who was at the party last night? (who is the subject)
To whom were you speaking on the phone? (whom is the object)

Note: "To whom" sounds very formal. In everyday speech you would likely say, "Who were you speaking to on the phone?"
He wasn't the man whom I saw yesterday. (whom is the object)

Verbs

Verbs are the action words. They make the sentence go. They allow a sentence to get somewhere. They are the swords that tell what the nouns and pronouns are doing, or what is being done to them, or what they are.
Ahmed makes a living as a landscape designer. He is very artistic.
Did you hear the one about the mouse that went to Scotland and became a moose?

The bad news is there are a lot of rules for verbs. They come in tenses (present, past, future, present perfect, past perfect, and future perfect) and moods (indicative, subjunctive, imperative). The good news is you don't have to know all the rules to be a good writer. If you suspect you might be getting twisted up verb-wise, ask for help and trust your ears; listen to your words and see if they sound right.

Verb Tenses

PresentI workI am working PastI workedI was working FutureI shall workI shall be working
Present PerfectI have workedI have been working Past PerfectI had workedI had been working Future PerfectI shall have workedI shall have been working

An important reminder: Be consistent in your use of tenses. When telling a story, for example, don't start off in one tense, then change to another.
<wrong> When Jamie was walking (past tense) down the street, he meets (present tense) Mabel.
<correct> When Jamie was walking (past tense) down the street, he met (past tense) Mabel.

Verbals

Verbals are parts of verbs used in sentences as adjectives (called participles), or nouns (called gerunds). The infinitive form of the verb, formed by adding "to" before the verb, may also function in sentences as other parts of speech, mostly nouns.

A participle is part of a verb (often ending in -ed or -ing) used to describe a noun or pronoun.
He rushed into the burning building to get his cat. I saw him running back out. He had the cat clutched in his hand.

A gerund is part of a verb used as a noun.
Smoking is not good for your health. Inhaling smoke will damage your lungs.

An infinitive is part of a verb formed by putting "to" in front of the verb. It is used as a noun, adverb, or adjective.
To smoke is not good for your health. (noun)
It is becoming more difficult to smoke cigarettes indoors. (adverb)

Because verbals share the characteristics of both verbs and other parts of speech, they can add interest and vigour to your writing.

Adjectives

Adjectives describe or tell you more about nouns and pronouns.
Mr. Fussell is a mean, cranky, unpopular man.

In this example the adjectives (in bold) tell you more about Mr. Fussell; maybe more than you want to know. Except the odd spelling trap, adjectives are easy. They can help your writing become more interesting and precise.

Adverbs

Adverbs describe verbs or tell you more about verbs or each other. They are used to express time, place, manner, degree and cause.
As he walked slowly down the dark street, the rain ceased very suddenly, and the moon gradually appeared in the quickly clearing sky.

In this exampled the adverbs tell you more about how he walked, how the rain ceased, and how the moon appeared and the sky cleared.

Here's another example, first, with not adverbs:
He turned and looked through the window at the leaves falling from the tree.

Then, with a few adverbs (bold):
He turned slowly and looked indifferently through the window at eh leaves falling softly from the tree.

Use adverbs in your writing to add colour and precision to your verbs. Adverbs answer such questions as how, when, where, how often, how long, how much, etc.

Function Words

These act like the glue in a sentence, connecting or joining the content words.

Conjunctions

Conjunctions connect or link words, phrases, or clauses to each other. They are used to help join ideas together.
Pat and Mike are good friends, but that doesn't mean they never quarrel.

Conjunctions enable you to combine thoughts into longer sentences, and to avoud a series of short, choppy sentences.

COORDINATING CONJUNCTIONS
(connect 2 similar structures: 2 nouns, 2 phrases, 2 clauses) and, but, or, nor, neither, yet, so still, for.

SUBORDINATING CONJUNCTIONS
(connect clauses to the main subject and verb) since, after, until, because, although, if, unless, where, when, while, as.

Clauses that begin with subordinating conjunctions should not be left to stand alone as though they were complete; they depend for their meaning on a main clause.
<wrong> If there were no gravity.
<correct> If there were no gravity we would fly away.

Preposition

Prepositions connect or join nouns or pronouns to the rest of the sentence. They show relationships of place (above, between, in, on, around, through, under, over), time (after, during, before, since, on, until), or manner (with, like, for, of). The noun or pronoun that follows a preposition is the object of the preposition.

He went to the movies; he got out at 9:30 and went into the restaurant.

Normally you do not end a sentence with a preposition in writing since its job is to connect a noun or a pronoun with the rest of the sentence.

It isn't necessary to memorize these descriptions of the parts of speech in order to write well. But they can be useful reference points. For example, a reader might suggest that your writing could be improved if you used nouns and adjectives more precisely. (Car is more precise than vehicle, and convertible is more precise than car.)

When you are writing you are trying to convey meaning as completely as possible with only the printed word, and no sound or sight to help. So the more precise or exact the words you used the more likely your reader will get the picture you are attempting to convey.

Sentences, Phrases and Clauses

Parts of speech are grouped into phrases and clauses, which in turn make up sentences.

In this section we look at ways to identify sentences, phrases, and clauses. One of the most common traps that writers fall into is using phrases and clauses as though they were sentences; that is, not giving enough information to the reader to make the meaning clear. In writing it is important to make sure the reader knows to what or to whom you are referring.

Sentences

A sentence is a group of words that is sufficiently self-contained to independently make sense. A complete sentence has at least one subject and one verb (predicate).
<wrong> Constantly washed by water.
<correct> A peninsula is a neck of land constantly washed by water.

Functions of sentences

To make statements. I can't yodel. - assertive or declarative
To ask questions. Do you like yodeling? - interrogative
To give commands. Start to yodel at once! - imperative
To express surprise or emotions. You don't know how to yodel! - exclamatory

Forms of sentences

A simple sentence has a subject and a verb. The subject is the doer of the action (when the verb is active); it can be thought of as who or what the sentence is about. The verb is the word that tells about the action the subject is doing. Every sentence has at least one subject and one verb.
John sat on the chair.
John is the subject of the sentence, doing the action; sat is the verb which tells what he did.

A compound sentence has two or more independent clauses joined by a conjunction such as the following: or, and, but. Each clause could stand alone as a sentence.
John sat on a chair and drank a cup of tea.
The typist prepared the report, but his boss took all the credit.

A complex sentence contains a simple sentence, called an independent clause, and one or more dependent clauses beginning with a subordinating conjunction or relative pronoun.
Spring, which begins March 21, is my favourite season.
The simple sentence or independent clause is Spring is my favourite season. The dependent clause beginning with a relative pronoun is which begins March 21.
The typist was skilled, but he still made mistakes.
The simple sentence or independent clause is The typist was skilled. The dependent clause beginning with a subordinating conjunction is but he still made mistakes.

Phrases

Phrases are groups of words without verbs. They are clusters of words that are not complete enough to be sentences; that is, they don't have both a subject and a verb. When verbs and other words are added to them, they can become sentences. There are several types of phrases:

Prepositional Phrases
to the hockey game
in the backyard
under the chair
behind the cupboard

These all begin with prepositions and tell you the location of something, but they cannot stand alone. They are incomplete because they don't have anything to which they refer. You don't know what or who is going to the hockey game.

Infinitive Phrases
To run away
To jump over a hurdle
To slide into first base

These are phrases that begin with infinitives. They cannot stand alone because they don't give enough information to make complete sense. Who is going to run away?

Note: You will sometimes see phrases stand alone in writing. Here's an example:
"Where are you going?"
"To the hockey game."

This makes sense because the answer refers back to the question. The reader understands that the words "I am going" have been left out. So phrases only make sense in a more complete context. They provide information or description but by themselves they are incomplete. In writing, make sure your phrases are connected to the verbs and nouns that complete their meaning.

Clauses

Clauses have both subjects and verbs, and may contain phrases. They can be independent, if they can stand alone and make sense. Simple sentences and independent clauses are the same thing.

They are dependent, if they need more information to be complete. For example,
I don't watch television programs that are violent.

The meaning of the clause is not clear without the rest of the sentence to which it refers. Here's another example:
Gardens in British Columbia are hosts for huge slugs, which have big appetites.

Taken from: George, Jerry (1994). Good Greif! Good Grammar. Markham, Ontario: Pembroke Publishers.