Okay, it's like this:
Say you just got a new toy and you're playing with it on the playground. Suddenly a big bully that you don't know comes up and takes it away from you. He tells you he's taking it because it's too new to be safe, but he'll give it back if you give him all your money. Then after you give him your money and he gives it back he tells you that you have to prove to him that it's safe by tomorrow or he'll take it away again and never give it back. And you'll have to pay him to look at your proof that it is safe. But he may not like your proof, so he may take it away again just because. But he'll still keep your money.