look for a local motorsports club. SCCA is a good place to start, but BMW, porsche, corvette clubs etc also have autocrosses.
if they have a beginners school, go to it.
when you go, sign up for novice or beginner or a class like that. when you go, check in at the front desk, and tell them it is your first time. they will probably help you through signing up for work, how to work your work station, and they probably also have instructors to ride along with you on your first few runs to teach you how to drive.
no matter how good a driver you are the street or track or go kart, you will be slow. you will be painfully slow. you will look at the cars and drivers killing you by multiple seconds, and go, wow, how the hell can they do that?
do not take this as discouragement, take it as encouragement. ask these drivers for advice, have them watch your runs, ride along with them, have them ride with you. that is how you learn.
i went to my first event 3 years ago in the 951, and this year won the local series in the STR class in my MR2:
