As far as I can tell it works something like this:
Place the Civilian Presence module on the map centred on where you want the civs to be and rotate and size to suit. Place Civilian Presence Spawnpoint module(s) where you want the civs to begin and place Civilian Presence Position module(s) where you want the civs to walk to.
Things I've noticed that may be helpful:
Spawnpoints and Postions need to be within the boundaries of the Presence modules size and shape, although the entire path the civs will take does not need to be
You don't seem to have to sync the modules together for them to work.
Civs don't seem to spawn if the spawn point is in LoS of a player.