I believe OP is trying to set up the WiFi for the first time, so there may not be any settings or a WEP key yet.
Is this a router you bought, or one that came from your service provider?
If it came from your provider, it may be noted on the housing somewhere, or you may have to call Tech Support.
If it's one you bought and you can't find the manual, search the web using your router's brand and model number and 'default password'. You should find sites showing manuals in .pdf format and somewhere in there you should find the default username and password as set by the manufacturer. It may be something as simple as:
Username: admin
Password: admin
From there the internal menus should help you find out how to set up the wireless and change the password.
The WEP security key is another step that protects your network from someone connecting and using your internet connection.