[rayiner]

If you say, get paid in Bitcoin, one transaction a month, and that's the only way you earn Bitcoin. Will you use the same source address all month?

[judk]

The payer uses a source address, which changes because each transaction should "kill" the original source, sending it's money to two addresses: the payee and the "change" that goes back to the payer but using a newly invented address.

You can invent a new destination address each time you transact (to get paid or to receive change). You make a new address by picking a random number and doing some math.