It's a keycode feature. You don't need to install additional software, but you do need to purchase the feature. Now, having said that, you need to look at your port allocation, and how many fax ports you have purchased. Again, largely a keycode issue, unless for some reason you have to add hardware for ports (usually the server is equipped with enough ports, but you have to buy the keycodes to enable them.)
As to documentation, if you already have CallPilot, check your documentation CD. There will be an Engineering pdf, Install pdf, etc.