,

The comma is a valuable, useful punctuation device because it separates the structural elements of sentences into manageable segments.

Use commas to separate independent clauses when they are joined by any of these seven coordinating conjunctions: and, but, for, or, nor, so, yet.

Using Commas

Wikipedia:Comma_(punctuation)

http://upload.wikimedia.org/wikipedia/commons/5/5c/Comma.png