How to switch between visible buffers in emacs?

If I am in split-screen viewing 2 different buffers on Emacs and the cursor is on the top buffer, what's a quick way to move the cursor to the bottom buffer?

Bonus question: if I know a command, is there an easy way to identify what key-combo it's bound to, if any?

To switch to other buffer use: C-x o.

Describe key: C-h k.

Here is a better solution when you open more than two windows(buffers) in one frame:

(global-set-key (kbd "C-x <up>") 'windmove-up)
(global-set-key (kbd "C-x <down>") 'windmove-down)
(global-set-key (kbd "C-x <left>") 'windmove-left)
(global-set-key (kbd "C-x <right>") 'windmove-right)

Now, you can use C-x UP/DOWN/LEFT/RIGHT to go to the above/nether/left/right buffer when you have three or more in one frame, they are more precise than 'other-window and you don't need to install any package.

You even CAN make it to cycle the buffers in the direction(vertically/horizontally) with one of the above shortkeys with configuration in .emacs/init.el file, but I don't recommend it(besides I don't remember it anymore, you can google it if you want).

Of course, you can use other shortkeys other than the ones I use in my .emacs.

You may also be interested in WindMove, which enables "directional" window navigation with <S-up>, <S-right> etc.

With respect to the bonus question, if you know the command (other-window), and you invoke it with M-x other-window, Emacs will show a brief message in the minibuffer stating: "You can run the command `other-window' with C-x n".

There is also M-x where-is which prompts for a command and gives you the current bindings that result in that command (if any).

There is a tutorial that's shipped with Emacs. It actually has the answer to your question (see the section MULTIPLE WINDOWS about 80% into the tutorial). The tutorial can be accessed via C-h t, or M-x help-with-tutorial. There's also a link to the tutorial on the initial splash screen of Emacs. Right below the link to the tutorial is a link to the on-line Emacs Guided Tour. The tutorial walks you through basic editing/movement commands, the guided tour is more of an introduction to what Emacs has to offer.

If you want to navigate among only buffers that are currently displayed, then you really want to navigate among the windows they are displayed in. This gives you a way to do that, using window/frame names that are the same as the buffers:

See https://stackoverflow.com/questions/4858958/better-window-navigation-in-emacs/7133190#7133190