Generally your first couple of days will consist of department training, company orientation, and then on-location training. In some cases it's not quite in that order, but you will generally complete all three training programs within the first few days of working.
Depending on which department you are working in, your experiences will vary widely. I personally work in merchandise, so what I went through is probably a lot different than what you go through if you are a ride op, which I am assuming is where you are applying.
If you start after the first day of the season, expect to come in at least 2 hours before the park opens to do morning training sessions. Until you learn to check restraints and things you will probably not be doing much but working entrance. After you have done basic training you can check restraints, etc., but you still can not "operate" the ride. In order to work controls you must first pass your visual boards test, which is basically a test of control procedures and what all of the lights and buttons mean on the control panel.
I personally know people who worked for 3 months and never even bothered to get certified on their ride, mainly because they didnt care if they got to work controls or not, they just liked checking restraints, etc.
Anyway, thats the short version of my answer. If you have any questions, be sure to let me know. If I can't answer them, I'm sure there is someone on here who can.