The SSID is the name of your wireless network. In order to use wifi on the Wii, you first need to have a wireless router for internet. The easiest way to find the SSID of your network is to go to a PC which has wireless capabilities, open up the "View available wireless networks" dialog and click "Refresh network list". This will display all of the wireless networks in range; the SSID you need is simply the name of the network corresponding to your wireless router.