there are 2 options to choose from. 1. Connect an ethernet cable to the back of your xbox and plug it into a wall input that has to be connected somehow to a computer. (this has the best and most reliable connection in my opinion, mobility is almost impossible unless there is a second outlet. These cables range from $30-60). 2. Buy a wireless router at any local electronics store (best buy, circut city, radioshack, etc. [I highly advise AGAINST getting a router from wal-mart, they are very unreliable, lag constantly, and lose connection almost daily, if not hourly.]) Hope this helps!:)
The first step is to connect your Xbox 360 slim to the router with an Ethernet cable. Find the Ethernet jack on the backside of the 360 and plug the cable in. Then connect it to one of the ports found on the back of the router. This will connect your Xbox to the internet letting you sign up for an Xbox 360 live account.