It’s basically portrait mode but without a new fancy phone.
Also, it's only currently available for iPhones 6S and up, and Android phones from 2015 and newer. Instagram is working on adding the feature to more phones. So for now, if you have an older iPhone or a kind of obscure Android, you might be out of luck.
In the Instagram App, go to “Stories,” and then go to the bottom where the options for “Live,” “Boomerang,” etc. are. Swipe left until you see “Focus.” Tap it.
BuzzFeed – Tech