Thi mode allows you to add/delete units on the map for the current player.
You can change the current player using the dropdown below the unit list
Selecting units, and then press Enter will open up a dialog for additional unit options, such as changing player ID, gemston amount, etc
Different types of units may offer different options in dialog
You can also provide string identifiers to units in the options dialog, which can be using for scripting and other things.
Example: In order for a gateway to teleport units to another gateway, you need to provide each gateway a string identifier and set up the destination gateway in the options