You have to make a shortcut of Blockland on the desktop, then right click the shortcut and click Properties, then in the target box, copy and paste this at the end of it
-mod editor
Then hit Apply then OK, then start up the shortcut, then start a server, then hit F11 for World Editor, or F10 for GUI Editor (I DO NOT RECOMMEND GOING TO GUI EDITOR, SINCE YOU MIGHT MESS SOMETHING UP)