Welcome!
It's pretty easy since you're starting with fresh water and hopefully no algae.
First off, with zero CYA, target FC is 3. So add 60 ounces of standard 8.25% bleach or its equivalent. You can eyeball half a jug. Just pour that in front of a return with the pump on so it disperses and mixes.
To protect that chlorine you need CYA aka Stabilizer. Targeting 40, poolmath calls for 72 ounces - 4½ lbs. CYA granules are sold in either 4 or 5 lb canisters. Get whatever size they have at your local big box hardware store or pool store. 4 lbs will take you to 36; 5 tp 44. Either is acceptable. Pour the whole thing in an old sock or nylon and set it in the skimmer basket or dangle it in front of a return so there's lots of water flow to dissolve it.
By the time you're done fumbling with that, the bleach will be well mixed. Add a quart of 31% acid. Poolmath actually calls for a bit more to lower pH to 7.2, but just in case your pool isn't quite as big as the manufacturer claims, you don't want to overshoot. Pour that quart in front of the return.
Now go herd the kids inside and get them changed. By the time that battle is done, the pool's ready to swim in. Probably too cold for you, but the kids'll insist it's fine through blue lips.
The CYA will take a couple days to dissolve completely. Day one, you have none, so target 3 FC. Day two most if not all the CYA will be dissolved, so assume it's around 40 and target 5 FC.
Day three, the sock should be empty, so remove it. You might need a pH adjustment again. You want to target about 5 for the FC. The goal is to add just enough each day so that FC doesn't dip below the minimum for your CYA before you test and dose again. In a few weeks, it will become very predictable.
That's it.
Pool School - Recommended Pool Chemicals tells you what chemical does what and how to add it
Pool School - PoolMath explains how to use poolmath to figure how much
Pool School - Basic Pool Care Schedule tells you what to do and when.
