How did the Vietcong use the lanscape to their advantage during the war?

During normal working hours, they (The Viet Cong-VC) were pumping gas at the nearest filling station; or selling groceries in the local supermarket; or selling motorbikes at a town store. At night they became guerillas. In the Forests/Jungles/Swamps they would have "caches" (hidden) weapons & ammunition. They would have tunnels to store medical/food supplies. Agent Orange was deployed to remove those Forests/Jungles and other vegetation used for enemy cover & concealment. During the TET Offensive of '68, they came out in the open and fought "as regulars" in conventional battle; they hardly existed anymore after TET. The NVA (Northern Regulars) took over the fight from 1969 onward.