Translation:If you have a cake, why don't you eat the cake?
Don't let this section get you down. It's, I think, a hurdle section, like a rite of passage. Once you get through it, then down the line you'll start to remember more and more of how Italian syntax works, plus more of its idioms will better better understand. It's a clever language, but can be a bit awkward to the logic of our English thinking brains.