How to create my own customized missions?

[leo.civil.uefs]

Its possible to take a map, put some units etc, and play it from the game itself? Like skirmish, I mean, me agaisnt pc.
I mean, I know we can modify the original missions by creating a mod and name the folder with the same original's mission name.

But what about to create a new map?

There is some way to play it after finished?

NOTE: Im not talking about multiplayer.