Both the tmux and GNU screen commands are terminal multiplexers. They allow you to have multiple windows within a single terminal window, and to jump back and forth between them. A window can be divided into panes, each of which gives you an independent command line.
|command|work|
|:–:|:-|
|> tmux |Start tmux session|
|Ctrl + b | Hotkey|
|Ctrl + b , %| Create new pane on side|
|Ctrl + b , “| Create new pane below|
|Ctrl + b , /