Unfortunately we didn't have time to implement a proper tutorial and some of the art assets are placeholders. I've added additional information on the game's page that explain certain mechanics. In the third level, you are supposed to drop the key plant onto the deposit. Once activated, the "Br" blocks will swap. Blue blocks aren't collidable (you will fall through them) while brown ones are. This will allow you to go to the right and get a mushroom. Use this mushroom to get back on the big plant at the start of the level and ride it down. On your way down you will notice a white rectangle. Jump into it and it will send you to the exit. It's a teleporter.
We're well aware that it's confusing, especially considering that some sprites are missing. Hopefully the additional info I've provided on the game's page can help out a bit. We'll likely come back to this sometime in the future and properly complete and polish it, like we wanted to.