Lettuce Turnip the Beet

Okay, so basically, the joke is a pun. You know, like when words sound the same but mean different things? "Lettuce turnip the beet" sounds like "Let us turn up the beat." A DJ is supposed to turn up the beat, and lettuce, turnips, and beets are all vegetables. I know you are not the sharpest tool in the shed, so I hope I didn't confuse you too much, dummy.