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I took Astronomy in college; got an A; and we studied retrograde motion - BUT I STILL DON’T GET IT!!!

It's easy, think of it this way... You're on the expressway, you're (Earth) in the left lane traveling faster than a car in the right lane (Mars). When you're a great deal behind the car in the right lane, it looks like that car is traveling forward just like you. But when you come up beside the car, it looks like the car is traveling backwards (yet both cars are obviously moving forwards, you're just going a little bit faster). And when you get sufficiently ahead of the car in the right lane, you no longer have the illusion it's going backwards.

Now pretend the road you're traveling is circular, and the analogy hopefully translates even better to what happens when Earth "laps" Mars every couple of years.