Let's say you only have a terminal or a SSH access and want to perform multiple attached commands at the same time. E.g: wget.
screenPress enter to start using CLI and enter your command.
To detach from your screen (and let the command run), press : Ctrl + a then d
screen -lsYou'll see a list of PIDs. If for example I want to take back the hand on 9623, I'll enter :
screen -r 9623