You just configure it and it works. How easy was that
But seriously, dude. You really have to learn to formulate your questions better. I highly
recommend you read this
. It's both interesting and informative.
On to your actual problem, you'll have to give a lot more info. For example, how does your ADSL modem connect to your computer (ethernet or USB)? Does it act as an autonomous node (firewall, router, gateway, DHCP server) or is it a software slave?