Firstly, you will not be accessing any "website" until the modem is configured, you simply dont have (as yet) an internet connection so how could you?
What the manual is telling you to do is to access the MODEMS configuration page which is done via the network and therefore has an address similar to a webpage's. The thing is, it is NOT on the web so you should not enter "www." just the HTTP and the address, usually something like "click here"
when you have got here you can enter your user name and password and specify which connections types you have and then save the settings to flash and reboot the modem. You should then be online.
If you are not able to access the modem at all then turn off any firewalls that you have running and try again. Still no joy? then make sure the lan connection is up and working and not turned off in the bios or similar.
Post back with any more info....