Grey,
Welcome to TFP.. A Great resource for all pool owners from Lost Wages...
No one can tell you for sure what each valve does because not every pool is plumbed the same way.. We can, however, make an educated guess...
So, my guess is this...
The valve in the top right side of your picture selects between the Skimmer on one side and the Main Drain on the other side. Unless marked, you will have to play with it and determine which pipe goes to the Skimmer and which goes to the Main Drain.
The next valve down is the "Intake" or "Suction" valve and it allows you to suck water from the Pool (Skimmer or Main Drain or both) and the Spa Drain. In the current position I would have to assume the Spa Drain is off...
The valve in the bottom right of your picture is the "Return" valve. It allow you to send water back to your Pool or Spa or both.
The valve on the left of your picture is a puzzle for me.. I assume one way sends the water through the filter, but I'm not sure where the water goes when sent the other way. I notice you have this one labeled as Spa Off, but that does not make sense to me.
A few more pictures might help along with what the labels say on each valve...
Thanks for posting a challenge...