I have a couple of doubts that I never understand the true meaning of some.
For exemple:

When some description about typefaces refer the feature: optical sizes, what the really difference from the types without this feature?

A good hinting of a typeface, really give much more legibility on the screen, but what are the techniques for make a really good hinting typeface?

This are two questions that occupy my head for some long.

I am most interested in knowing the answer to these questions, and the more detailed the better.
if you lose your time to answer me, thanks a lot!