"Unselecting" a Selected Unit

[JohnS]

I have read the manual, such as it is, and watched a bunch of tutorials. After about 4 hours of play, I still cannot resolve what should be a ridiculously simple problem. Sorry for having to raise this.

Once I select a unit, left click on it, how do I "unselect" it ("deselect" it, if you prefer) ????

In other games you hit "Escape" but here that brings a menu that does not address this issue. In some other games, you simply click on an open space such as a river but here if I have selected a plane or artillery battery I find myself targeting something when all I wanted to do was to leave the current unit and move on to another unit.

I hope that I have not somehow simply missed something that is buried in the pathetic manual or in the hours of tutorials but if you folks can help me out here it will be much appreciated.