Slitherine

When one clicks on "Play Order of Battle" you can then at the next screen click at the top right of the screen where it reads "Check for new community Content" the brown crate looking thing hovering the mouse over this displays this message - which is only seen if you are connected to the internet here you can install community stuff the only catch is you may not and probably will not see what you installed unless you exit out of the game and restart it .... took me 5 min or so to figure this out ...

And you can remove the content the same way, BTW.

Some of the stuff available there is really, really old. Like a couple of my very first scenarios.
Also, the official Battle of Britain mod is currently broken, will be fixed in upcoming patch.