It pings the user.
They will get a notification if they enabled it and basically be notified.
A red number will appear on their screen on the server or user logo.
They get the attention of the person with a red 1 on their server icon, most usually mark as read, but some who do view them, these are done for important purposes only, no one likes this,
Hey , this guy <- at mentioned, how you doin
Hey, this guy <- You’re cool, be my friend pls.
Impatient people will most likely flip you off, kindly also in the reply section turn of the ping off, it is hella annoying.
If a person has do not disturb on or has notifications off, a ping will bypass that and still give them a notification, good for getting their attention.