Select File->New, leave all default values and press OK.
Hit CTRL-K, and CTRL-F to turn off the skybox and fog respectively.
Select Object Placement mode. Go into environment->gameplay and select the starting_position object.
Turn on the terrain type overlay through Overlay->Terrain Overlay. The read area is the playable area (where you can put starting points).
Place a starting position for both Player 1 and Player 2 (use the right sidebar menu to select which player the starting position actually belongs to).
Make sure you select the proper starting position.
Select a gameplay->strategic_point_flag object. Place 2 or three of them around one of the starting positions.
Now use Shift and drag to select the 2 or three strategic flag points that you’ve created, copy them, move them to the other position and re-arrange them appropriately (if necessary). Paste (ctrl-v) and three newly created strategic points should appear at their former locations. (You may wish to use the grid option to make sure that the points are at a similar distance from both starting positions)
Select gameplay->strategic_objective_struct and place it in the middle of the two starting points.
Save the map. The files mentioned above will be created.
Congratulations. You’ve now created a fully functional (yet bland) MP map.
(Optionally) Open up the <MapName>_icon.tga file in your favorite image editor. Save it as a <MapName>_icon_custom.tga file. Now you can edit the file. To your hearts content.