If you are talking about an AOSS access point (AOSS should be labeled on the box of your wireless USB adapter) then you have to install the software, plug in the USB adapter into a USB port into your computer. Then go to Settings under Wii Options on the bottom left corner of your wii menu. Choose Internet, Connection Settings, Connection 1, select AOSS and there should be instructions on the screen.
If you have the old Wii, you are going to have to choose "Search for Access Point" instead if "AOSS" isn't there. I wouldn't know what your access point name would be, so you are going to have to find that out after installing the software.
If you are talking about the Nintendo Wi-Fi USB connector, there are complete instructions in your Wii Manuel.
To find your friend code, go to your Wii Message board and choose the thing in the bottom left corner and the right icon, then choose Address Book and it will show your console number.
Welcome to WiiChat by the way.