Arrow keys / WASD to move 0 to open the editor 1, 2, 3 to change the layer you are drawing Click on something in the panel and then click on the ground to place. You can use an autobuild like feature by clicking space and dragging your mouse on the ground while the editor is open
I followed @griffpatch 's tutorial for this. The only thing that is different is that I used a different sprite for the player. Go follow @griffpatch right now or you are bad.