To find it, go to the message board (by clicking the thing that looks like an envelope on the bottom right corner on the
Wii's main menu) then click the the address book. Then, click the - button on your
Wii remote, and it will say something like
Wii Number: <tons of numbers>. Those tons of numbers are your
Wii number.
To add people, go in the address book, and there should be an option to add a friend or something. Get their
Wii number, and put it in. They also have to add your
Wii number. It will take a couple of minutes to work as well.
Sorry if my instructions aren't detailed enough.
I don't add people very often. >_<