Thank you for your feedback and suggestions! Regarding the level editor, it's probably easiest if you start small - start by loading an existing level and just play around by moving some objects a bit. Maybe try to delete some stuff. As long as you save the level with a new name you don't have to worry about messing things up. I think after a while you will find that the level editing is pretty easy, it can even be fun in itself :)
Maybe this video can be a good starting point: