The PC should be connected to the router with a network cable. The cameras should also be connected to the router with a network cable. If you have not enough network ports on the router, you can buy something called a switch and connect that to the router. The switch basically extends the number of network ports your router has. A network switch works more or less the same as a power strip or a USB hub. It gives you more places to connect devices.
You also of course have to power the cameras. For some cameras, this means using the included power adapter. However some cameras support PoE which means you can power them through the network cable by attaching one end of the network cable to a PoE switch (and the other end to a camera).