How can i split my internet connection by using a switch?

A modem is not enough; you need a router that can do NAT. Virtually all "SOHO routers" do this. Just replace the modem with (a compatible) soho router, setup the login details etc., connect both computers, maybe reboot the computers (or repair their network connections if you know how), and it should work. Alternatively you can setup a second network card on the PC, connect the laptop to the PC with a crossover cable (or a switch and two cables), and setup NAT on the PC, but that would be more awkard to both setup and use.