Move with arrows or WASD. Press 0 for level editor. In the level editor, keys 1, 2, 3 and 4 for selecting tiles. Press E when your mouse is over a tile to select it for the level edition. Press 0 to go back to the playing mode. When you are in the edition mode, you can press "R" to reset the level (answer the questions to make sure it's not a mistake and to give the correct value to the width and the height of your level), or you can also press "L" to choose one of your levels, as you can save more than one. Have fun!
Thanks so much to @griffpatch for his helpful tutorials on youtube.
