Changing key bindings + rebinding keys + what function is C-x C-h bound to?

[gnuist006@hotmail.com (gnuist006)]

I want to remove a key binding such as ESC-d and instead put a whole
range of key bindings

ESC-d a
ESC-d b
ESC-d c
etc.

Or remove key binding such as C-d and replace with a whole range of
key bindings such as

C-d a
C-d b
C-d c
etc.

While on this, can anyone tell what function are the keys
C-x C-h bound to although they give all key global bindings.
I could not find what it was bound to using describe-key and
so is a little tricky.

keywords:
rebinding keys