How do I get a list of commands starting with a certain key (combo) in Emacs?

Question

I can use C-h c (describe-key-briefly) and type a key combination and it will return me the function bound to it. But I\'d also like to type only a

Answer 1

Do the key combo then C-h. For your example of C-x, do C-x C-h. This also works with sub-maps, e.g. C-x r C-h to see everything under C-x r