You type in the ip address of the router in a web browsers url, usually 192.168.0.1
and enter in the user name and password of your router, it will usually be admin for both the user name and password or admin for the user name and the password will be kept blank. You can find the user name and password by searching for your model number and brand. Once in you can change any setting you would like, from forwarding a port to setting up a dmz or putting security on. I would recommend WEP2/personal as it would offer the most secure network.