Hi Jo Ann, welcome! ⚜
Folks here will give you great advice, but need information first. A good test kit tells you/us what your pool has or needs.
The links posted above are great references to start with.
No doubt you will need liquid chlorine (bleach) either from the pool supply of WM or the household section. The household kind needs to be plain, no additives, no chlorox. And uses twice as much as the pool type.
There is a date on the bottle 19 174 (means yr and day of yr) you want the most recent date you can find to get the best strength.
In my case, while I waited on my test kit to arrive, I dumped a gallon of bleach in every day and kept my filter running 24/7.