A compound sentence is made up of two or more main clauses that are joined by the coordinating conjunctions for, and, nor, but, or, yet, and so.

• I came, I saw, and I believed.

In this sentence, there are three main clauses - I came, I saw, I believed, joined by the conjunction and.

• Paolo tells a joke, but Nena does not laugh.

The two main clauses Paolo tells a joke and Nena does not laugh are combined by the conjunction but.