I seem to be stupid but, I'm not having any progress in this game. Straight at the beginning, I can run in a cricle, or will fall down into the pit, where I can't escape from, because I can't jump up the walls.
I don't know exactly what the issue you're having is so forgive me if what I suggest sounds obvious.
Holding the jump button makes you jump higher (if you're on keyboard) and will help you get past most basic jumps.
Killing green slime enemies spawn a smaller green slime, this is not an enemy and will work as a moving spring.
Hope this helps, and thank you for trying out Sinher! ♥