2-5, what Red said.
You always have to spend all the money in an account (address) at once.
I have 10 BTC in Address1, I want to pay you 1 BTC.
Address1: 10 BTC
Address2: 1 BTC (this goes to you)
Address3: 9 BTC (this goes to me - the change)
Address1: is now empty.
A cool side-effect here is that anyone analyzing the transactions can't easily tell if I paid 1 BTC or 9 BTC. (assuming they know I have Address1, but don't know who has Address2 or Address3)