If I did the password wuold I have to put in a password everytime I open the computer? I like just opening it and it being there and ready.
You should only have to enter it in once and from then on your computer would have access to your wireless.
If you don't do this, your neighbors can use your internet connection freely.
How do you tell it to only accept connections from my IP addresses, and what is MAC?
I wouldn't worry about doing that as it is fairly complicated and your routers security setting would block anyone that didn't have your password anyway.
A MAC is a mac address. It's the address of your paticular network card.
Every network card, including wireless, has a specific address that no other card has.