The valves are , low point drains for the hot and cold water lines, a drain for the fresh water tank, these should be closed, and I'm going to have to jump back and forth to figure them out.
Closed is cross ways from the pipe run. Sorry I'll be jumping in and out trying to get this right.
This is best guess.
Left side, hot water line low point drain, closed ,except during winterizing.
Center front, fresh tank drain, closed , except to drain fresh tank.
Center rear. fresh tank fill, when city water is hooked up, open this valve to fill the fresh tank , do not leave un attended , close when not filling on board fresh tank.
Right side, cold water system low point drain , closed except when winterizing.
Note the valves for draining do not drain the hot water heater , it has to be by-passed at the tank and drained there. More valves for you to find , back side of the tank.
Note, If you look up from underneath the RV you should see all these lines, after the valves are open to drain on the ground.