Use commas in compound sentences before these coordinating conjunctions: for, and, nor, but, or, yet and so. Also use commas to set off introductory clauses, phrases and words from a sentence's main clause or to separate non-essential clauses and phrases mid-sentence.
Insert a comma to separate two or more coordinate adjectives describing the same noun or three or more words, phrases or clauses. Use commas for geographical names; for example, "Denver, Colorado." Additionally, insert commas to set off items in dates and addresses and to separate a main discourse from a quotation.Learn more about Writing