Lovely explorable explanation here: https://ciechanow.ski/curves-and-surfaces/

That whole blog is 10/10 and has some of the best explorable explanations I've seen.

holy crap this is wonderful

A favourite explorable from sometimes back – by Alex Berke (memory just sparked looking at the link above!) http://www.beautifulsymmetry.onl/?pageName=cover

Beautiful 🙂 I once worked on Catmull-Clark subdivision; a site like this would have helped me get started!