can anyone tell me how to make a square tileset eg. turret defence mods, sunken defence mods. i'm nooby lol.

Are you sure you're not referring to maps? I don't know of any mods with a square tileset. If you're referring to maps, download an editor such as SCMDraft and use that to place individual tiles of terrain.

Get SCMDraft. Go into terrain editing mode. Look at the top of the screen. There will be a few drop-down menues. One will say either "Isometrical" or "Cut/Copy/Paste". Change it to Rectangular. Then place terrain.