conjunctions

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.

source : http://www.englishclub.com/grammar/conjunctions.htm