These instructions are for Ubuntu 8.04, but they really haven't changed because they relate to how wireless works, not to how Ubuntu works.
https://help.ubuntu.com/8.04/interne...onnecting.html
Usually, all you need to enter is the SSID (That's the network name as created in the wireless router or access point) and the key (that's the password you have configured for the wireless security.
If you did not set up the security, do so.