In the editor, by default everyone makes maps, it's much easier than modding.
But straight to the question? What mods?
The editor enables you to make them, but information surrounding the existence and possibly usage of mods is still not there...
You basically play "maps" if you play online, but what determines your selection of mods?
Is it something that's enabled by overriding it before entering the game client, thus rewriting the game?
Or is it a function you can select in-game to tweak melee maps to some kind of custom settings?
If that is all, then I will be surely disappointed in the system.