1. Download from the forum thread.
2. Extract the zip file, Copy the "Battleforge" folder and place it into your "Documents" folder.
3.Click the "pluginbasededitor" , accept TOS terms.
4.If you have BF already installed than go to the main folder and if you don't have a map editor in there copy and paste the one provided in "Map Editor" folder you just downloaded.
5. Thats it just play  around with the map editor now enjoy!.

6.If you don't have a battleforge folder you need to download it there are 3 links in the same thread, download all 3 and follow instruction.

Download - create a battleforge folder whereever you like, extract the first zip inside of it, and than create another folder and name it "base" go inside "base" and create yet another 
folder and name it "Pak", take the 2 other files and extract em into "Pak"