Welcome! There are a lot of details figure out, for sure. Best bet is to take pictures, lots of pictures! You'll want to get some of the pool itself, the equipment pad and electrical. Post them here, and we can guide you better.
As for statistics on the pool, is it above ground, in ground, what kind of liner, approximate dimensions, last known status, and anything else you can tell us about the pool and property.
Glad you are starting here!
Some links for info: ABCs of Pool Water Chemistry PoolMath <--- use the app... or online calculator PoolMath <--- to see how much of what to add for clear healthy swimming pool! (be sure to use YOUR pool dimensions) Test Kits Compared To do any of this, you need a great home test kit!
In my signature below I include the link for adding your pool details (size, type, equipment, test kits, etc) to your signature That helps immensely, and keeps you from having to repeat those details over and over again!