Commas are used to separate or clarify relationships between sentence parts to make the meaning of a sentence clear and easy to grasp. In this lesson, you'll learn how to commas to separate independent clauses, items in a series, items in a date or address, two or more adjectives preceding a noun, and contrasting elements and words that interrupt the flow of thought in a sentence. The last section of the lesson explains how to use commas in the greetings and closings of a friendly letter.