I'm looking for my first road bike in many years. Want to do what I can to get the best fit.

What is the correct (or optimal) way to determine if a particular frame geometry is suitable for your body? I ran the Competitive Cyclist fit calculator and don't really understand the results, other than learning I need a top tube of 51-52cm. I realize there's bike "fitting" and bike "sizing", and it's the latter that I'm looking for. I don't know how to measure the ideal stack and reach or other pertinent measurements.

Thanks,
Robert