In many ways, Bitcoin mirrors how we transact in cash offline. With cash, you can transact in a fully peer-peer manner. If you go to buy a pack of biscuits in a shop, that transaction is only known to you and the shop attendant at that point in time.

Bitcoin addresses are unique ids used for sending and receiving Bitcoin. To send an email to a friend, you need their email address. You will then send them an email from your own email address.