Integrator
Let’s say you have two maps, Map1 and Map2. In your .GAM file you can click twice to plop down two boxes. In the first box, select your first map file; select a tile set; select a monster, character, and sound set. Define an entry and an exit point on the map. Do similarly for box 2.
Then you can draw a line from the game's title menu to the first box, a line from the first box to the second box, and a probably a line from the second box to your “game over” sequence, if any. Click on the starting point, and add a title graphic or animation; change the text at will. Do similarly for the ending point. And then export.
There’s your game. Simple, but functional. The title menu leads to the entry point in Map1; the exit to Map1 leads to the entry to Map2; the exit to Map2 leads to the game over screen.