C-h b keybinding should have probably been among the few things that I should have initially learned when I embarked on Emacs journey. Nonetheless, better late than never. If you are starting out on learning Emacs then you should etch this keybinding because it opens up a mini buffer and shows all of the emacs keybindings available acorss all the modes.
This is extremely useful for when I forget or want to know a key binding for something. Saves me a google search :)