"Maria had the day off from work, so she watched an Orange Is The New Black marathon on Netflix."
In this lazy (and super-relatable) compound sentence, a comma and the conjunction so are used to join two simple sentences.
"We should call a repairman to fix our washing machine; it keeps shredding all of our underpants."
Here, two simple sentences are combined with a semicolon. Ooh, fancypants. (Unlike the poor panties.) Semicolons are a great way to show off your mastery of sentences; just remember to save them for when the two sentences that you're connecting are closely related in content.
"June's favorite actor is Al Pacino, yet she's never seen The Godfather."
We're going to make you an offer you can't refuse: learn how to build a compound sentence. Here, the comma and the conjunction yet are used to join two simple sentences and create a compound sentence.