[rjfvillarosa]

Best scenario.
On a shelf right next to the CAT5 cables you would place your modem and router, connect both modem and router to the electrical supply, (not switched on) plug the modem into the phone socket then with a small ready made patch/cat5 cable you connect the lan port on the back of the modem to the internet in port on the back of the router, now by process of elimination you will need to plug one of the cat5 cables at a time into the router to see which in house socket they activate, if you had a twenty four port switch you would be able to connect them all but they run at about $100 so we are assuming you are using a standard 4 or 6 port router.
Switch on the electrical supply after you have connected the modem to the phone socket and the modem to the router.
If you are already using the modem you should not have to make any changes when you plug it into the router and like wise with the router it should automatically start supplying signal to each lan port, the cat5 cables to the wall sockets can be plugged and unplugged with eveything running.
Using a laptop you can walk around the house plugging the cat5 cable from the laptop into a wall socket and if the icon in the bottom right (telling you that a lan cable is unplugged) goes off you know that socket is live.
After all is said and done try and turn the shelf with the modem and router on into a cupboard to stop the ingress of moisture and dust.