What is a private key (private keys) Bitcoin?

Transfer or move the Bitcoin is indeed very easy, but in the rear screen, movement and storage of Bitcoin is actually done with something called the ' private key '. The easiest way to fully understand this, is to imagine a traditional post box system: Imagine if Maria wanted to send a letter to Peter. First of all, he needs to know the address or number of the post Peter. Vice versa, if Maria wanted to send the Bitcoin to Peter, he must know the address of the Bitcoin Peter, that is the number that specifically indicates that the mailbox belongs to Peter. This number is called with the address of the wallet (wallet address), or the public key (public key). This number is very long and complicated because of the many mail boxes Bitcoin on the world, but fortunately you don't need to stop, you can see it on the internet. So now Mary sends Bitcoin to postbox Peter. Let's suppose the number mail boxes Peter is 2034. Maria can look into this and see postbox Bitcoin t