You may buy tickets at the resorts, but to have any annual passes activated, you must to that at the parks.
All MYW tickets are biometrics, which means that the 1st time you go through the gates, the bone structure of you hands (distance between the 2 fingers) is measured. Then everytime you go back, it is checked against the 1st reading. The correct way to do it is to place your right index and middle fingers into the machine so that they webbing between those fingers is flush against the black knob, then squeeze tightly. Make sure to always use the same hand everytime you enter.