There are a few ways, one is to start the sim, once you use it the prompt will ask you to either insert the keys then or later, no matter what you're going to have to do it. One is to call the number, the other and easier is to take the key it came with. Now if you call make sure you have a LARGE sheet of paper, you will be read many many codes, then you will be reading them back and another code process will start. Now if you have the Gold or acceleration pack you will have to do the same thing,. If you have changed computers or the name of the computer or reinstalled the process will be repeated as with most software. Since Microsoft sold the FSX platform to Lockheed you may have to keycode an internal security file. The directions are online.