MySTified3k, what you rent from the cable company is the modem. You still need that. This router is use between the computer and the modem. What router basically does is keep your ID like password or whatever. So instead of your computer doing all the ID verification, the router now do it. And router also have some firewall protection. And the most popular benifite of router is this is where it split to other PC. So you can use multiple PC without save ID verification on any of those PC.
I hope this help.