I have some experience with this. On the general screen, there are buttons for adding maps, editing, exporting and stuff. when you add them, they appear on the stack to the right. When you want to edit a map, always do it from the campaign editor so when you save a map it automatically saves it from the campaign. Then you can make buttons for the maps. if you have any more questions, just ask.
On the Loading Screen Tab, right click in the white box and choose, "add button". Then type in the title you want to show up, the map file loaded, and whether or not that button will be visible the first time you open up the campaign. You can make them visible in game with the "Game - Enable Campaign Button <number>" trigger or whatever it is.