What am I supposed to test for? How often?

It is recommended to test your water at least once per week, when there are no issues with clarity, algae, or other problems to be addressed.

At a minimum, you should be testing for Free and Total Chlorine, pH, and Total Alkalinity.

There are other parameters that should be tested monthly, such as TDS, Clacium Hardness, Cyanuric Acid (CYA), and metals; but a visit to a trusted local pool professional can perform those tests for you, usually free of charge.