It's basically a jumping round and your not being judged it's like a feeler for you and your horse for the course🏆
You aren't judged in a schooling round. Basically, you go in by yourself and jump your course like you were going to be judged, but it isn't for points.
It is a round, (kind of like a blue/red class), that is used just to warmup and get your horse in the show ring. So basically a warmup round.