So this will depend on: how many cables of cat5 are there? Where is your router now (do you have internet now?). How many Ethernet ports are on your router?
So you have a router in your office, and there's an Ethernet jack righter there and you want to wire up two rooms, all you need to do is run a wire from an Ethernet port on your router to the outlet, put a switch where the other cables are (where the phone and catv is), and crimp the cables. Connect the other rooms with said switch and the crimped cables. Done.
The reason most use patchpanels instead of going straight to a switch is cost. Most of the time you have more wires than you actual want to connect so you use the panel as an interim. If you ever change your computer room to another room for example you can swap cables around between them quickly. A panel costs $15 where as a switch with 12 ports is gonna be around ~$150.
You could just have a dangling mess of wires of course if you don't care. As for a diagram, the panel comes with it's own punchdown tool and instructions. You just split the wire apart, put them over the right sockets and press down with the provided tools.
As for the ethernet cables
https://www.youtube.com/watch?v=482VtesZwZ8 you will need, as said previously, a crimper (as cheap as $15 but for a little more you can get full kits with correct end pieces etc.), preferable borrow a tester to make sure the cables work,
and if you go with a panel of course a spool of bulk Ethernet cable ~$50 otherwise you don't need it.