Here're the keys used in the editor:
-/+: switch between levels (the zero in the corner indicates which level you're editing)
Tab: open and close the object list
^ (in your case): switch between editor and in-game
s: save level (I think the smiley indicates if there're unsaved changes in a level)
1/2: change layer (the only point of this is if you want to have several objects on top of each other)
arrow keys: adjusts the initial direction of the tile you're currently hovering on. The little arrow in the corner tells you the current direction of the tile you're hovering over.
It's all fairly confusing because I made the editor for my own use, but hopefully this helps! :)