I won't try to explain the difference between a switch and router as you can read about it at any website that deals in them. Just think of the switch as a splitter.
We have Cat 5 through our whole house, which is connected to a router (wired) that runs off the cable modem. I would like to have additional ethernet connection in my room, so can I hook up a 2nd router (or ethernet switch? not sure which one) in the house to the rj45 cable via cat 5?? And what is the difference between a router and a ethernet switch?