My brother got an Xbox 360 for Christmas and I decided I wanted to make an account buy drugs online so I made an xbox live account on the internet and now I don’t know how to sign in on the system. All it says is join xbox live. HELP!

I currently have the Xbox Arcade system. I am planning on purchasing the Xbox Live starter pack for it. It comes with an ethernet cable. I have no internet connection in my house, but i have wi-fi and a Sprint Buy Viagra Online Without Prescription Air Card, and my computer is a laptop. Is it possible and how do I connect my system to Xbox Live through that. Is there anything else I need to buy?