It's usually used when you are surprised to learn something. Other uses are to add how serious you are being about something. The last and most obscure usage is to explain the status of a couple. They are "For Realsies" if they are officially dating.
The same as fo'real but was instead created by Crabstickz; from Youtube, in his last 'Advent Calundah' video before Christmas when almost falling over.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"