Arrow keys to move. 0 to ender/ exit editor mode. Keys 1-4 to change selected category. The same keys to change selected tile. Click to place/ delete tile. Get to the box filled with green to win. Do not fall out off the world or run out of health. L to load a level. S to save a level. R to reset a level. Find levels here: https://scratch.mit.edu/discuss/topic/541730/
Thank you Griffpatch for your you-Tube tutorial. (I didn't follow your tutorial step by step.)
