A compound sentence contains two independent clauses that are combined (or joined together) by a comma and a FANBOYS (for, and, nor, but, or, yet, so). Looking at each of these, which looks like this example: Dogs are considered to be man's best friend, but some people prefer cats over dogs. You are looking for a comma with one of the FANBOYS (coordinating conjunction) RIGHT AFTER THE COMMA, and whatever comes after the comma must be a complete sentence.
