Doesn't Bell just give you the modem? Normally if they do all you do is simple plug the modem to the WAN port on the RT-N56U and you got a wireless internet. Of course you will need to set up your router for better protection.
Normally there's a CD that comes with it, use that CD on your computer to set up a password for your router to prevent anyone but you to access your internet.
These days it seems like the larger ISPs are providing router/modem combinations, but the rogers ones can be put into bridge mode (acts like a modem and disables all router functions) and I'd be surprised if the fiber op ones can't as well.