How are you connecting? Wired or wirelessly? I am a PC user but once you manage to connect to the router successfully, in your web browser type in http://192.168.0.1 or type in http://192.168.1.1 to access your router configuration page and set it up for use on the Internet. Also, do you have a router connected to a modem and the modem connected to the cable plug in your wall?
Its a wired only modem as far as i can see. Turn on your computer and modem, grab a cat5/cat6 cable and plug it in to the ethernet port. On your mac the symbol may look like this: <--->
Plug the other end into the yellow modem port, which should be the same. On your mac open the system preferences icon and click on "networks". Click on "built in ethernet" or similar. If the round button next to that is green, you should be ready to go. Here is an article that may be helpful: http://support.apple.com/kb/HT1383
Hope this helps
PS I am running OS X Snow Leopard (10.6.8) so some parts may not apply to your machine
PPS Look at your instruction booklet that came with the modem, or download a manual from the internet.