쉬다. 쉬고있다, 쉬는중이다. 쉬고 있어요. 쉬고 있어. 쉬어요. 쉬는 중 입니다. 쉬어.
don't try to find rules. It makes learning language more difficult. preposition, postposition, all the other suffixes are really a lot. so the best way to know it is speaking, reading, and writing a lot and have a lot experience. Korean also can't organize it. And there are so many exceptions. just try to get familiar with it through speaking a lot. then you naturally feel it when you use something wrong it feels weird.