I finally understood what to do lol.
So first you only have the grab ability. Grab an enemy to aquire its power. The boxer gives you the boxing ability. With that you can smash crates. You first have to select the ability in the menu though. Then you can go to the ninja in the bottom right corner of the map and get a sword. With the sword you can cut bushes. From there its more of the same: explore, grab abilities, repeat.
The blue chests contain additional hearts for which you have to buy keys for 20 wood.
Ok game but needed more guidance imo.