Need Port Forwarding To Play Counter Strike On Server - How To Do It?

Port forwording means... when an incoming connecting is comming to your router, it will forward that perticular port or set of port to specific local IP.
since you have internet conncetion which has single ip like 10.1.12.123 but in your local network several computers are connceted to that router. now if a CounterStrike request is coming to your network how router will know that where to send that request. so if you router is configured to forword perticular port to your machine only. your machine will be accessible over internet using that port.