A comma, is “soft stop” cuing readers to temporarily pause if they are reading out loud. Commas also separate clauses in long sentences and connect ideas.
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.