So instead of memorizing A squared plus B squared equals C squared for a right triangle, you regularly spend fifteen minutes measuring the sides and angles and doing trig to figure it out? There are a ton of formulas you end up memorizing, and you either do it because you used it so often that you memorizes it, or you practice memorizing it. Though it is often a mix of both, of you repeating it in your head a bunch of times, and then also practicing it in actual problems.