Definition: The phrase "sit down" is a verb that means to take a seat or to lower your body onto a chair, bench, or any surface where you can rest. It can also mean to invite someone to take a seat.
"Sit down with someone": This means to have a serious conversation or discussion.
"Sit down and shut up": This is a more informal and sometimes rude way to tell someone to be quiet and stop talking.
"Sit down" is a simple yet versatile phrase that you can use in many situations, whether you're inviting someone to take a seat or expressing your need to rest.