Setting up another tv with a tv signal splitter?

I have comcast xfinity cable and internet. tv uses a box so i can get ondemand.I have another cable box and another tv that id like to use in my family room so that i can watch one thing and other members of my family can use the other tv to watch what they want.I want to know how to hook another tv using the other cable box and not mess up my internet in the process.I want to do this myself if possible.calling comcast is to exspensive for me right now .can someone tell me exactly what i need to purchase and how to do this i need step by step instructions. thanks.