It's easy man.
Go to Macintosh HD-->Applications-->Utilities-->Open Network Setup utility, make sure your router is hooked in, take note of the gateway it shows you in network setup utility. Open a web browser(I recommend Firefox). In the address bar type in the gateway, it should be an ip address example: 192.168.1.1 that should get you to your router's web interface, then you need to type in the username and password, it's usually something like
username: admin
password: admin
or maybe password as the password or something like that. Your manual hopefully will have all of that information. Once you are logged in you should be able to configure the security settings and what not.