This is very basic, just shows you how to get the distance and object selection right.
Use left mouse to place turrets along the road. Rightclick will destroy the turrets and also enemy jeeps.
Jeeps spawn every 7 and 3 seconds, the second one has more "HP". Check out the objects alt. values.
Mouse over enemy jeeps to see the current HP value on the bottom counter.
Turrets have a range and will always aim and shoot at the closest target.
Feel free to play around with it.