Yeah, custom tiles are a little confusing. Basically, when you have a custom tile selected, whatever happens to balls is what that custom tile will do when placed. The easiest way to get a grip on them is: Make two custom tiles. Name one something, leave the other as new, or call it level or something along those lines. Select the named one, place some stuff down (e.g. make something that a normal block doesn't do, like doubling in a straight line, or sending everything left except stuff from the left). Then select you new again, and put the block you made down.
