It is hard to explain all of horse behaviour. Just keep on paying attention like you are already doing and you will learn by yourself. You can also read a lot of horse books or look up some good horse trainers on youtube (be careful to be critical though because not everyone who claims to be a horse trainer is necessarily a good one, but if you go through multiple ones you'll start to see what is okay and what is not. I think Monty Roberts is quite good. Think like a horse channel on youtube is also really educational so you should definitely check it out).