I'm trying to understand the topic of blockchain and bitcoins as well. So, the only one question I want to get answer for: how do exchanges commit orders? I mean, how the transaction could be started by exchange? As I understand, only the owner of wallet (with the pair of pub/private key) can start transaction for transferring some amount of btc. So, I can't find the information about "remote control" of wallet. Maybe I am wrong, please correct me. And excuse me for my English. It's not my native language.
In general, if an exchange wants to execute a buy or sell order without asking you, the relevant Bitcoins need to be held by an address that the exchange controls. When an order executes, and Bitcoins change hands, nothing changes on the blockchain. The only thing that changes is a record internal to the exchange. It's only when you withdraw the money from the exchange that anything changes on the blockchain.