Pressing C-h a will run the emacs function
apropos-command which makes emacs prompt for words (or a regexp) to search for. It will then show a buffer containing a list of names and descriptions related to that topic, including key bindings for each of the functions available via keystrokes.
Pressing C-h m (
describe-mode) gives a buffer describing the major and minor modes in effect, including listings of available functions and their key bindings.
Pressing C-h b (
describe-bindings) gives a buffer listing all current key bindings. The listing includes global bindings as well as bindings for the active major and minor modes in the current buffer.