Downloaded a lot of them? Great! Haven't downloaded any? Don't worry, there are 3 available together with the mod (all the 3 made by me, of course). And what about now? Open the editor and go to "Tiles" and "Custom". If you though "Why would I go there if I don't have any custom tileset?", then look at this:
Now select the tileset you wish and click "Transfer". This will happen:
Note: I'll also add a "Delete tileset" button, in case you don't like it.
Thanks for reading and I see you in my next post!
EDIT: Remember when I said I was going to add a "Delete tileset" button? Well, I made it:
EDIT 2: Fixed the "succesfully" instead of "successfully".