In other words, anyone and everyone can flag a post (Just press the three little dots in the bottom right, and click the flag that shows up.) On it’s own, it does nothing, except possibly mark it for a moderator/admin to have a look at. If it’s flagged 3 or more times it will be hidden, so it will appear as being flagged and hidden, and you have to press a button to see it. A mod/admin will look at it and if a rule has been broken, delete it and/or punish the person responsible. If not, I assume they can unflag/unhide it in the event it’s just 3 or more people being dicks.
You might get something flagged without warning, but unless you’ve broken a rule or 3 or more people decide you said something immoral, nothing will happen. If you DID break a rule, and you’re punished, I’m sure you’ll be made aware of it.