|Did it come with a user manual? The most common way to configure these type devices is to open a browser and log into the router admin interface by entering it's default IP. With Linksys I believe it is 192.168.1.1|
I have a Dlink and it uses 192.168.0.1
There is usually a default User Id and Password.
Your manual will give this information.
In some you need only set the WAN to autodetect and it will find the internet. In others you must manually input the necessary settings. It also depends on your ISP. Some will tie the internet connection to the specific MAC address of the PC to which it was connected. If that happens you need to clone that MAC in the router.
Unfortunately you will get little help from most ISPs
If you need to input manual settings you can obtain this information by re-connecting Modem direct to PC and in a Command Prompt window run the following
Write down or print out the results.
Goin' Fishin' (Some day)