how to connect two PCs for gaming?

To connect directly from one PC to another, you will need a crossover network cable, and for the first 3 sections of you IP address to be the same, also your subnet should be the same.

For more than one PC I would say buy a switch as it will auto-negotiate the type of connection and cable, same story with IP settings for this.

Connecting all the pcs you want to play with to the same router and create a local game. And all pcs running the game will be able to join and play together.

Can even be done without internet connection using a hub to connect them through ethernet. If you know what Im talking about you should have no problem getting it to work.

So connect them to the same router/hub/switch then get a computer to start a "local game" and get the other pc(s) to join that game.

Good luck

Gumby