Help with the Lunar Magic editor for Super Mario World

I just downloaded the editor for Super Mario World, but I don't know how to actually change the levels.
I can open up an image of a level with the text "Entrance to Level 105" on the editor and from there I assume you should be able to click on a sprite in the menus and simply add it to the image, but nothing happens.
I browse through the editor menus and pick all kinds of options, but I can't do anything with them, I just keep getting this message "Nothing selected to paste!".
How should I start using it to actually be able to change the levels at all?

I have read some guides that say you are supposed to see a "TEST" text and some invisible mushrooms when you open a new level, but I just see a level from the real game and whenever I try to highlight something it is only highlighted while I hold in the mouse button, and the Delete button doesn't do anything either.