Newbie - Please help with pool filter valves

Hello - I will forever in your debt if someone can help me figure out the way my pool works.....

Just moved into home with Anthony & Sylvan in ground plaster pool. It has a D&E filter, a water purifier, two skimmmers, two bottom pool drains, and a return line for a polaris 360.

My problem is the valves on the pump. I'm not convinced that I have them set up properly.

When I have the pool drain and skimmers open, I get no pressure into the skimmers. Can I only run one at a time?

Should the pool cleaner valve (return line) be open when I run the skimmers or pool drain?

When operating the Polaris 360, my pressure goes from 12 to 25. Is that normal? The only way I can get it moving is to shut off the pool return drain completely. Should I use the eye-socket dealies to plug up the other return lines, instead of manually closing the pool drain return?

I apologize if I am being confusing. I have 4 valves on the pump - one for skimmers, one for pool drain to filter; one for pool cleaner, and one for pool drain return. My basic question is what do i open when.

How is the pool motor? If you can get the specific model, HP rating and approx age that would be good. If not, use descriptive terms like "piece of sh*t". That was useful info from the guy who did a pool inspection for me in determining the pool motor needed replacing at the house I was buying.

** Interesting that a different guy that was my home inspector made the same exact comment about the 21 yr old hot water heater in the basement of the house. Is it me or the house?!

LOL. The pool is 8 years old, and the motor seems to running well. (knock on wood). I don't have the other info handy, but can re-post once I get it.