What must the writer add to the sentence in order to make create a compound sentence

A compound sentence has two subjects and two verbs. You use a coma and a coordinating conjunction to combine two sentences into one compound sentence. EX: It was cold outside, so he put a sweater on. In this sentence, we used a coma and so to combine “it was cold outside”, and “he put a sweater on”.
*HINT* an easy way to remember to conjunctions can be using the acronym F.A.N.B.O.Y.S for and nor but or yet so.