Photos and videos are synced with your Instagram account. This app is also compatible with a private Instagram account, so you don’t need to have a public Instagram profile to share on this app.
With privacy and safety in mind, Instagram allows you to keep your account private. When your account is private, only people you approve can see your photos and videos on Instagram. Lean More (official help)
Many people have created new private Instagram accounts, in order to utilize this app. Once you’ve linked the app, you only need to post photos and videos on Instagram, and of course the viewers only need this app to see the posts.