1. Use a comma to separate two independent clauses joined by a coordinating conjunction (and, but, or, yet, for, nor, so). See CS, however.
  2. Use commas to separate the items in a list.
  3. A comma is required after the penultimate (second-last) item in the list: “God, Adam, and Eve took their evening constitutional in the garden.” This comma is sometimes called the Oxford comma. See OC.
  4. Use a pair of commas (or dashes or parentheses) to separate a subordinate clause or parenthetical expression from the main clause.