Use the valve to isolate either the one pipe on the left, or the two pipes on the right, see which way stops the flow of water into the skimmers, that side is to the skimmers and the other side is the bottom drains.
As far as to the "normal" position, I keep my floor drain and skimmers open all the time. The floor drain pulls colder water from the bottom and helps to keep the pool temperature more even, and of course the skimmers collect floating debris.