How is the British monarchy funded?

I'm having a hard time understanding all this stuff about the Civil List, the grant-in-aid and the Crown Estate and I need somebody to explain it to me like I'm an idiot. From what I have read, the monarchy hands over a LOT of money to the government, only to get a little in return. If that's the case, why doesn't the monarchy just keep their money? I don't understand. Please help!