In a compound sentence, each sentence contains two independent clauses, and they are joined by a coordinating conjunction (such as ‘and’, ‘but’, ‘or’) with a comma before it.
“I raced to the movie theater, but it was too late.”
Or, as George H.W. Bush famously said:
“I have opinions of my own, strong opinions, but I don’t always agree with them.”

A compound sentence contains two independent clauses that are connected by a coordinator or joining word. A compound sentence can join both independent clauses or complex clauses. These coordinators, or joining words can be easily remembered by the acronym FANBOYS,  which stand for the following: FOR, AND, NOR, BUT, OR, YET, SO.

Unless it is a very short sentence, coordinators are preceded by a comma. A compound sentence can also be separated by a semi-colon.  When this is the case a joining word is not used. Here, each clause by itself can be a complete sentence.

examples of the compound sentence

I went to the shops, but I did not buy anything.
I went to the shops; I did not buy anything.
Famous quotes which are compound sentences:
“A man may die, nations may rise and fall, but an idea lives on.” – John F. Kennedy
“Government does not solve problems; it subsidizes them.” – Ronald Reagan

A compound sentence is used to express more than one idea in a sentence, although they must have a relationship to one another. Compound sentences make reading more interesting.