Safety
Nobody can message you unless you agreed to it. Anything here can be taken down.
Somebody is bothering you
Block them and they disappear from everything you see — their posts, their replies, their profile in search. It is instant, needs no reason, and they are not told. Report them as well if the account should be looked at; blocking fixes it for you, reporting fixes it for everybody.
There is no open inbox here, so a stranger cannot write to you. They can ask once, with a note saying what about, and you decide. Saying no is silent and they cannot ask again.
Something needs taking down
Report it from the post, reply or profile itself. Reports go to a person. If somebody is being put at risk — named, located, threatened — choose Somebody is in danger and it comes out of public view straight away while it is looked at.
If somebody is in danger right now
Quad is not an emergency service. Call 911, or 988 (suicide and crisis) or Text HOME to 741741 (if you would rather text than talk). Your campus public safety number reaches a building faster than an ambulance can find one — worth having in your phone.
Report the post afterwards so it stops being public, and tell the person you noticed. That last part is the one only you can do.