Simply stated, a conjunction is a word that connects other words or groups of words to make sentences. You can use a conjunction to link words, phrases, and clauses, as in the following example:

I ate the pizza and the bread sticks.
Call me when you are ready to go.

Coordinating Conjunctions

You use a coordinating conjunction (“and,” “but,” “or,” “nor,” “for,” “so,” or “yet”) to join individual words, phrases, and independent clauses. If a clause can stand alone as a sentence, it is an independent clause. Coordinating conjunctions can also be referred to as coordinators. Note that you can also use the conjunctions “but” and “for” as prepositions.

The highlighted words in the sentences below are coordinating conjunctions:

Stella and Harriet are sisters.
Sassy, my dog, loves to be petted, but hates to having her nails trimmed.
Sassy refuses to eat dry dog food, nor will she drink warm water.

In the sentence below, the coordinating conjunction “but” is used to link two independent clauses.
Peter's father wants to be a railroad engineer, but he has never been to college.

Subordinating Conjunctions

A subordinating conjunction is a word which joins together a dependent clause and an independent clause. A subordinating conjunction introduces a dependent clause and indicates the nature of the relationship among the dependent clause(s) and the independent clause(s).

The most common subordinating conjunctions are: after; although; as; because; before; how; if; once; since; than; that; though; till; until; when; where; whether, and while.

What is a dependent clause? It is a unit which contains a subject and a verb. For example, “It was raining” is a dependent clause; the subject is “it,” and the verb is “was raining.” A dependent clause is a clause which cannot exist on its own; it needs a independent clause to go with it. For example:
Because it was raining, I drove my car.

This sentence contains two clauses, “Because it was raining” and “I drove my car.” The first clause (the dependent clause) does not mean anything on its own. If you were to say “Because it was raining” and nothing else, people will not be able to understand what you mean. However, “I drove my car” is an independent clause - we can understand what it means even if it is alone.

Joining clauses together with subordinating conjunctions:

Because it was raining, I drove my car.

The subordinating conjunction used here is because. It is used to show the relationship between the two clauses. A subordinating conjunction usually comes at the beginning of the dependent clause, but the dependent clause itself can be before the independent clause (usually followed by a comma) or after it (sometimes following a comma). Here are two examples:

Although it was raining, he was not wearing boots.
He was not wearing boots, although it was raining.

After he had learned to drive, Bill felt more independent.
In the sentence above, the subordinating conjunction “after” introduces the dependent clause “After he had learned to drive.”

If the book report is turned in on time, your grade will be announced on Tuesday.
In the sentence above, the subordinating conjunction “if” introduces the dependent clause “If the book report is turned in on time.”

Stacy had to begin her report over again when her computer crashed.
In the sentence above, the subordinating conjunction “when” introduces the dependent clause “when her computer crashed.”

Many people choose to believe in evolution because they don't believe the creation account in the Bible.
In the sentence above, the dependent clause “they don't believe the creation account” is introduced by the subordinating conjunction “because.”

Correlative Conjunctions

Correlative conjunctions are pairs of conjunctions which work together to coordinate two items. They always appear in pairs. This means that you use them to link equivalent sentence elements. The most common correlative conjunctions are “both … and,” “either … or,” “neither … nor,” “not only … but also,” “so … as,” and “whether … or.” (Technically speaking, correlative conjunctions consist simply of a coordinating conjunction linked to an adjective or adverb.)

The highlighted words in the sentences below are correlative conjunctions:

Both my grandfather and my father served in the Army.
In the sentence above. the correlative conjunction “both … and” is used to link the two noun phrases that act as the compound subject of the sentence: “my grandfather” and “my father.”

Bring either a salad or a dessert to the party.
In the sentence above, the correlative conjunction “either … or” links two noun phrases: “a salad” and “a dessert.”

Charlie is trying to decide whether to go to into the Air Force or to go into the Army.
In the sentence above, the correlative conjunction “whether … or” links the two infinitive phrases “to go into the Air Force” and “to go into the Army.”

The movie portrayed not only the school but also the surrounding neighborhood.
In the sentence above. the correlative conjunction “not only … but also” links the two noun phrases (“the school” and “surrounding neighborhood”) which act as direct objects.

Please note that when either is used without or and neither is used without nor, it acts as an adjective or pronoun.
Either car seems to be a good choice. (adjective)
Either seems like a good choice to me. (pronoun)
Neither car was good. (adjective)
Neither was good. (pronoun)