Stormtrooper: My lord, what should we do with all this beef?
Palpatine: Stew it.
Stormtrooper: My lord, what should we do with all this beef?
Palpatine: Stew it.
Alright listen up, buttercup. This joke is a pun! The Stormtrooper asks Palpatine what to do with the beef, and Palpatine says "Stew it," which sounds like "Do it." It's funny because Palpatine is a Sith Lord, and "Do it" is like, his catchphrase. You probably have a catchphrase too, like "I don't get it" or "Can we watch Paw Patrol again?"