I made a custom map, saved it, and tried to load it on Skirmish Single player, but when I click on 'Custom Maps' nothing shows up. Can anyone help me with this?
Are you sure it was saved in the correct folder? It should be the default folder when you save using the editor.
Make sure you click on custom maps in the Skirmish mode for it to show.
DMUK
Have you maked sure your in the right section? If its a space map you should be looking in Space Skirmish mode not Land Skirmish.
Make sure the map is set as Multiplayer and that it has at least two players. You can change this under file->map properties