Assuming you are referring to a drive-in movie theater:
Before the movie starts, you'll want to make sure your car is in good working order. Fill up the gas tank and check the oil level. You should also bring along snacks and drinks for the evening.
When you arrive at the drive-in, find a spot that will give you a good view of the screen. Once you've parked, turn off your headlights and tune your radio to the station that is playing the audio for the film. Some theaters may require you to use an FM transmitter.
Sit back, relax, and enjoy the show!