If one wanted to send a Bitcoin from Person-A to Person-B, then Person-A would go to their Bitcoin wallet. Send the Bitcoin to the wallet belonging to Person-B using the blockchain, which verifies the transaction. Each wallet uses a series of unique letters and numbers to identify it, much like a social security number. The blockchain is a mutual distributed ledger. A blockchain transaction is verified by many nodes, once 51% of the nodes agree the transaction goes through. There is no single point of authority for the blockchain, therefore no one controls it other than its peers, the distributed network.