Fish,
I see your plumbing a little differently than Mike... But only you will be able to tell for sure...
Pump B is your main pump and runs both the pool and the spa.
Automated Valve 6 is called your
Intake valve and selects if the water coming into the pump is coming from the pool (Pool mode) or from the Spa (Spa mode).
Automated Valve 3 is called your
Return valve and it selects if the water leaving the heater goes back to the pool (pool mode) or back to the spa (Spa mode).
A is your heater
E is your Cartridge Filter.. Inside are cartridges that captures all the floating junk that falls into your pool. The filter needs to be opened and cleaned at least once and year and maybe more depending on your pool.
D is called a Tab feeder" where you put chlorine tablets. Water runs through the feeder and dissolves the tablets and releases the chlorine into the pool.
11 is where the water goes back to your pool.
C is a booster pump for your pressure side cleaner. It gets its water from 8 and sends it to the cleaner via pipe 9.
10 is just a normal hose bib that is used during construction, but can be used with a garden hose to drain some pool water if desired.
F is a secondary pump that could do several things.. It could be for some water feature, like a large waterfall or it could also be for running the spa jets.. It gets its water from pipe 12, but where that pipe is connected depends on what the pump is for. Only you can tell us that. The output of pump F goes to a manual Jandy valve that sends the water back through pipes 14 and 15.. Again, only you can tell where the water is going. Currently the valve is sending water to both pipes 14 and 15..
G is your spa blower, which add bubbles to the water.
H looks like an old piece of junk to me..
You really do not want to manually turn any of the automated valves.. Some of them can be manually turned, while some cannot.. I suggest that for the time being, you don't screw with them..
As a test, watch your Intake valve 6 and your Return valve 3, and put your automation system into the Spa mode and see how they turn. Put the system back into the Pool mode and they should turn back to their original positions.
Good luck with learning your new-to-you pool.
Show us some pic of the pool itself and we might be able to answer a few more questions.
Thanks,
Jim R.