No offense, but you should lock the topic, download paint.net(google it) then go into your documents, open blockland folder, then open addons, copy the .zip called decal_default, go make a new folder somewhere, then open the zip and empty contents into that folder, open paint.net, then open that decal and edit it.
And I suggest that you look at other people's decals to get an idea of what kind of quality is legit around here.