It's meant to be sharing in the moment, kind of like Twitter but specifically for images. A lot of organizations use it for marketing and various forms of outreach, e.g. music venues will post concert flyers on Instagram. there are hashtags but no categories beyond that. you are also kind of stuck with the algorithmic "feed" for viewing, you can't group accounts you follow into categories or playlists. The app encourages you to make multiple accounts for such a purpose, and gives you an easy way to switch among them.