If you followed my tutorial, use the Blockland + Mission Editor.bat file to start BL, the Editor wont be shown in the add-ons menu since it isn't an add-on, rather something created specially for TGE.
If you DIDN'T use my tutorial, search for a post titled "The last mission editor tut needed" in Mapping Help, then follow the links to the .bat since I'm too lazy to link for you. After you've started with the .bat file press F10 at the main menu, if you've done everything right some gray boxes with text on them will appear around the screen (this is the GUI editor).
