I'm new to pools-Am I supposed to have two drains?

This all started because when I would vacuum the pool it would suck down to the bottom and I couldn't break suction without turning off the pump. The guys at the pool company said the main drain probably wasn't connected in and that's why the suction was too high. So off I went trying to get the drain into the loop.

I have a 20,000 gal inground, and I have two valves coming out of the ground by the pump. One is open and that comes from the skimmer. The other is closed, and I assumed it came from the drain at the deep end. When I open that valve, water flow stops cuz it's sucking air.
I tried putting a hose into the pipe by the pump with the valve open and the pump off and it never seemed to fill up the pipe and overflow into the strainer basket at the pump. Next I swam to the bottom and put the hose into the drain in the deep end. I could hear gurgling, but again water never came up into the basket. At this point I went to the skimmer and I could feel cold water coming out of a port in the upper part of the skimmer 180 degrees across from the suction port that goes to the pump.
I appears that my deep end drain goes up to the skimmer. I'm not sure where the second pipe at the pump goes to.
Thanks in advance for your help