just lists all processes running on the system.
is very different. It is a BASH built-in. It shows jobs that a user or script explicitly put in the background.
press Ctrl-Z while a process is running to suspend it to the background.
use bg jobnumber
to resume the process (in the background)
you can start a job in the background by appending a &
$sh somescript.sh &
the script will start in the background and you will continue to have a bash prompt.
any job will stay in the BG until it finishes or is brought the the fore using fg jobnumber
this allows you to start and control multiple tasks
You can read more:
BASH Job Control