Your PC's must be in the same subnet then the router.
If the router's IP is 192.168.1.1, then your PC's could to be at 192.168.1.2, 192.168.1.3 and so on.
Mask should be 255.255.255.0 and gateway 192.168.1.1
Primary DNS is also 192.168.1.1, leave secondary blank.