According to Instagram, “Following a hashtag is just like following a friend. To get started, search for a topic you’re interested in or tap on a hashtag from any post. You’ll see relevant hashtags displayed in your search results along with related accounts. When you find a hashtag you like, open the hashtag page and tap on the follow button.”
For those wondering what the difference between following a user and a hashtag, hashtags usually comprise of posts by different people who might use the hashtag. This means that if you wanted to see Instagram posts that are related to pets, then you could follow the #pets hashtag, or #beach if you wanted photos of beaches around the world, and so on.
This also helps users cut through unwanted posts, where typically the hashtag you follow will post things that are relevant (we hope).