tmux is a terminal multiplexer. It lets you switch easily between several programs in one terminal, detach them (they keep running in the background) and reattach them to a different terminal.
For more information, check out their github page
Use [Ctrl+B] to start most commands
[%] – Horizontal Screen Split
[“] – Vertical Screen Split
[Arrow Keys] – To move between panes
For more commands, check out this cheatsheet