There is a lot one can learn about water. It's up to the individual to decide how much of that is vital to the brewing process. My level of understanding is very basic, and it works for me.
Many of the calculators are excellent. Martin's is quite popular here. I use Brewer's Friend only because I don't have a computer and BF is web based, I can use my phone.
Don't believe that the well water of a famous brewing city is what that brewery uses. They may and probably do treat it.
Martin has great suggested profiles to start with, based on the style you are brewing. To start off, it's ok to assume store bought RO is all zeros and 7 pH. It might be 8pH but the residual alkalinity will be so low that you won't be too far off. Then using the calculator you can play with how much of what needs to be added to get close to the suggested profile. I use CaSO4, CaCl, MgSO4, and NaCl. Lactic for most beers, Phosphoric for lihht flavored lagerd.
Then enter your grain bill and find out how much acid you need to hit your target mash pH.
A pH meter is handy for verifying that you achieve your target, then you can figure our where you flubbed up, or make adjustments in the future.