How do i get custom maps to work?

You probably saved it to the wrong folder. You'll have to move it/save it to the main directory of GC2 into the

Drive: GalCiv2/Twilight/data/custom maps/(map name here)  folder.

thats where it is saved yet it dosnt show up

nvm the folder was in a different area and to avoid these constant posts    is there a manual for all this? cus i still dont know where to put custom improvements (no folder for it as far as i can tell) and when i try to use my custom tech tree the game crashes

Use the mod folders OR create one in the mod dir.