This is a very old map editor. Use the new map editor instead:
What do they do?
The left edge of the display features the player selection and enable buttons.
"P" buttons
Those buttons marked P[number] (e.g. P4) allow you to select a player to edit.
All structures and vehicles that you paste on the map will belong to the player selected at the time of placement.
"e" buttons
Those buttons marked e[number] (e.g. e5) toggle the display of structures belonging to that player in the map views.
A note on Scavengers
Some Warzone 2100 multiplayer maps feature Scavengers. You can include Scavengers in your maps, but there are several limitations.
Scavengers must take up the slot occupied by player 7, and because of this they can only appear on maps featuring fewer than seven players.
Scavengers will not appear in One Player Skirmish games.
If you place Scavengers on a map, be sure to give them a factory, a power generator and an oil derrick. This will allow them to build units. Without these three buildings maps featuring Scavengers may not work properly.
When you use Scavengers always check and make sure that if you are doing, say, a 4 player map, that you do not enable any player after 4 except 7. So you would only have player e0. e1, e2, e3, and e7 pressed in. Make sure that players e4, e5, e6 are not pressed. If you dont you will get an error that says one or more players do not have trucks when you try to compile.