Help!!! Annoying weird notification pop up

[AC Question]

People of the Internet, I need help. So I recently got a Samsung s6 and it's been got but yesterday somehow this weird notification thing has been pooing up. It does it for apps like Facebook, WhatsApp, snapchat. It's a square that pops up on the tip center of the phone and you can slide it to dismiss or tap it to open. Please help me as this is so annoying