Ubuntu tmux default installation shortcuts

Install

sudo apt install tmux

start tmux

tmux

Note that [0] 0:bash is displayed below

split screen

Enter two sets of shortcut keys in turn: Ctrl+b, Shift+5 namely: %

Split screen up and down

Enter two sets of shortcut keys in turn: Ctrl+b, Shift+' that is:" 

Switch windows (note: mouse click has no switching effect)

Switch to the previous window: Ctrl+b, Shift+[    ie: {

Again

You can see that the cursor has returned to the first window.

Close the window exit, or Ctrl+D

Basically enough.