tmux is a terminal multiplexer: a software that allows multiple Windows inside one terminal window.
All command are preceded by a prefix key:
b) by default.
|Split screen in half from left to right|
|Split screen in half from top to bottom|
|Kill current pane|
|Switch to pane in whichever direction pressed|
|Toggle full screen of current pane|
|Switch to window N|
|Detach from tmux, leaving everything running in the background|