Begin by spending this evening reading Pool School. Take notes on the section Test Kits compared and decide if you will order a TF100 or some other suggested kit which probably also must be special ordered. Then bookmark the Chlorine/CYA chart and the Pool Calculator.
You will need to test the pool to find out the pH and the TA. Also test FC, CC, TC, and CH (see Pool School for what those are). The pool store can usually do that for you but don't let them sell you anything just yet. Pool store testing is sketchy most of the time but it gives you a starting point. You can fine tune after you get a recommended test kit.
You will need to buy CYA (stabilizer) and chlorine (bleach or liquid shock product). You may need to buy some other things to adjust pH and that will be done first so get that test data ASAP.
About 30 minutes after you get the pH correct, you can add stabilizer and perhaps a few hours later the bleach. Go on and calculate how much stabilizer you will need to get to 50 ppm, you will only go from 0 ppm to 30 ppm at first, but you want to have enough on hand for later. You will read in Pool School exactly how to do this, I'm just giving you the highlights, so you know what you are looking for.