It took me a few minutes too. I was convinced for a moment it was broken, but it's just not immediately obvious how the game works. All you can do is walk around and pick stuff up. You pick stuff up by clicking and holding the left mouse button, which will cause that thing you thought was going to eat you to slowly float over there and bring it back to you. As such, you can pick things up from afar. The E doors are fake, only the door at the end of the level is real and it requires no button press.