Terrain Marker(s)

(1) Click a truck, then hold CTRL and click on the spot on the map that
    you want to mark.

(2) Next, hold ALT and the key that you want for that spot.
    EXAMPLE: ALT N  (for a place at the north part of map)

(3) EXAMPLE: SHIFT N would take you to that spot on map (north map area).

You can have more than 1 Terrain Marker.

Terrain markers are handy for your outposts and enemy outposts on stock
maps (original fight for oil maps that came with the game).

Go here to look what the manual said