A conjunction

A conjunction is a word that "joins". A conjunction joins two parts of a sentence.
Here are some example conjunctions:

Coordinating Conjunctions Subordinating Conjunctions
and, but, or, nor, for, yet, so although, because, since, unless

We can consider conjunctions from three aspects.
Form

Conjunctions have three basic forms:
Single Word
for example: and, but, because, although
Compound (often ending with as or that)
for example: provided that, as long as, in order that
Correlative (surrounding an adverb or adjective)
for example: so...that

Function
Conjunctions have two basic functions or "jobs":

Coordinating conjunctions are used to join two parts of a sentence that are grammatically equal. The two parts may be single words or clauses, for example:
- Jack and Jill went up the hill.
- The water was warm, but I didn't go swimming.

Subordinating conjunctions are used to join a subordinate dependent clause to a main clause, for example:
- I went swimming although it was cold.
Position
Coordinating conjunctions
always come between the words or clauses that they join.
Subordinating conjunctions

The short, simple conjunctions are called "coordinating conjunctions":
and, but, or, nor, for, yet, so
A coordinating conjunction joins parts of a sentence (for example words or independent clauses) that are grammatically equal or similar. A coordinating
conjunction shows that the elements it joins are similar in importance and structure:

Look at these examples
- the two elements that the coordinating conjunction joins are shown in square brackets [ ]:
I like [tea] and [coffee].
[Ram likes tea], but [Anthony likes coffee].

Coordinating conjunctions always come between the words or clauses that they join. When a coordinating conjunction joins independent clauses, it is always correct to place a comma before the conjunction: I want to work as an interpreter in the future, so I am studying Russian at university. However, if the independent clauses are short and well-balanced, a comma is not really essential:
She is kind so she helps people.
When "and" is used with the last word of a list, a comma is optional:
He drinks beer, whisky, wine, and rum.
He drinks beer, whisky, wine and rum.

The 7 coordinating conjunctions are short, simple words. They have only two or three letters. There's an easy way to remember them - their initials spell:

F-For
A-And
N-Nor
B-But
O-Or
Y-Yet
S-So

A subordinating conjunction joins a subordinate clause to a main clause.

The following is a list of the most common subordinating conjunctions.

after, although, as, because, before, how, if, once, since, than, that, though, till, until, when, where, whether, while

An adverb clause is always introduced by a subordinating conjunction. A noun clause and adjective clause sometimes are.

Adverb clause: Before you go, sign the log book.

Noun clause: He asked if he could leave early.

Adjective clause: That is the place where he was last seen.

A subordinating conjunction is always followed by a clause. Many subordinating conjunctions can be other parts of speech.

Adverb: Jill came tumbling after.

Preposition:Jill came tumbling after Jack.

Subordinating Conjunction: Jill came tumbling after Jack had fallen.

I hated this lesson when I was at school ^_^

thanks Aden for this lesson ,it's very important to now it otherwise the language will be destroyed