It's quite easy.
If the map dont have it's own installer, copy the following "file extensions" to these folders:
.umf --> To the
*:Mobileforces/Maps-folder.
.utx --> To the
*:Mobileforces/Textures-folder.
(and if there is a tune attached)
.umx --> To the
*:Mobileforces/Music-folder.
*=your harddriveletter where you installed MobileForces.

And the maps automaticly shows if you use "skirmish" mode in singleplayer.
If you want to play them in a map rotation, you have to edit your INI-files.