Conjunction

Conjunctions are joining words: they connect words, phrases, or entire clauses. There are two general kinds of conjunctive words: coordinate and subordinate.
Coordinate conjunctions join elements that are grammatically the same: two or more words, two equivalent phrases, or two equivalent clauses. The most common coordinate conjunctions are: and, but, or, for, nor, so, yet.

• Red and white (two equal words joined in a phrase).
• Taking walks and looking at nature (two equal phrases in a relative clause).
• She ran to the corner, but she missed the bus (two equal clauses in a complete sentence).

A correlative conjunction is a special kind of coordinate conjunction. It connects equivalent elements, but it works in pairs of words: both, and; either, or; neither, nor; whether, or; not only, but also.

• He wants both money and power.
• Neither money nor power matters.
• Either she will go, or she will stay. 

Subordinate conjunctions. While coordinate conjunctions connect equal grammatical elements, subordinate conjunctions introduce dependent or conditional clauses.

• Although she has money, she buys few luxuries.
• Because he was late, he missed the train.
• After the movie is over, we shall have dinner.

Other word uses. Words that normally operate as conjunctions can often be used in other ways: as adverbs, prepositions, adjectives, or even pronouns.

• We have met before. (Here before is an adverb).
• Before they leave, let us have dinner. (Here before is a conjunction).

There are other words besides conjunctions that serve as connectors (or connectives) in sentences. The relative pronouns who and which are often so used.

• That is the man who was speaking to her.
• The dessert is strawberries, which give him a rash.

Some of the conjunctions work both as adverbs and conjunctions in the same sentence. This is often true of consequently, however, therefore, and nevertheless.

• He was ill; nevertheless he went to work.
• She disliked work; consequently she lost her job.

Note the semi-colon [ ; ]. This is standard here but is non-standard before but or and. (This appears to be changing, as speakers and writers treat words like nevertheless as conjunctions.)
It is possible to make clauses with conjunctions into separate sentences, especially when writing for literary effect.

• He did it. And he was glad.
• Stay away from here. Unless you want trouble.

In the second case the clause is so obviously dependent that it would not stand alone as a sentence and make sense. It can only be written that way for emphasis or some other effect.

source:http://babelnet.sbg.ac.at/themepark/grammar/conjunction.htm