install it like you would anything.
put the disk in the drive and auto run will kick in and auto launch setup.exe or double click the setup.exe with steam you just click the install button and it does it for you.
Make sure your computer is a gaming computer. Is you don't have a gaming PC then you will pay for a game that will not run or that will run very slow. Most computers that you buy locally are not gaming computers.
Oh, if from Steam then you download the steam software and then use the Steam application to pay for the game and download it. It cost $19.99 http://funadvice.com/r/3lv9c29q9m
I don't have it yet, I want it but would like to know how to install I think someone told me steam or something but I have no idea
How did you get it?