Welcome to the forum! You can possibly swim the first day your pool is full. (assuming you are filling from city water and not well water which sometimes has some different adjustments that need to be made.) If you will test your fill water, we can better see what you will need to do. Use a drops based test kit - no teststrips.

Post results for FC, TC, PH, alk, calcium hardness. Pick up several jugs of plain, unscented bleach, and some cya. You may be able to find it at Walmart, Lowe's, or Home Depot, or you may have to buy it at a pool store. Just don't let them talk you into buying a bunch of other stuff. It may be called conditioner or stabilizer, but if the ingredients say cyanuric acid or isocyanuric acid, that is the right stuff. Post your results and then we can decide if you also need to buy some Borax and baking soda. Don't add anything to the water before it is tested.