NAMING AND UPLOADING A MAP
Go to your 0AD folder, then go binaries -> data -> mods -> public. Then unzip public.zip. Go to maps -> scenarios, and all current maps should be there. New maps you make with the Atlas editor will also be saved to this folder, regardless of where you tell the editor to save.
There are two files per map, the .pmp and the .xml. To name your map, open the xml file in notepad or another text editor and the name and description sections are very near the top. To find your map in game, select the "all maps" tab when viewing scenarios and any new maps will show. To share your map, just zip those two files and upload to any normal downloads site.