This is an interesting category, and depending on the teacher the definition of gentle can vary greatly! Gentle yoga will often offer modifications and a less challenging pose as the primary pose. For example, instead of high runner’s lunge, the pose will be with the back knee down, instead of starting in a high lunge and giving the option to lower the knee. Props are often used but not necessary. Gentle classes will often attract people with less range of motion and the props can come in handy then.
I’ve been to and taught gentle classes that never have any standing poses in them, and I’ve been to other “gentle” classes that left me a sweaty mess. Gentle classes can be a good place to start and get used to poses, and tend to move slower than a flow class while still using the same poses. As with any yoga class if you go to a gentle class and find that it isn’t as gentle as you hoped, find another class and teacher instead of giving up. The teacher and their style and intensity is critical to finding a good match for you.