It’s built on the source accounts you give us. We engage their followers, people already interested in what you do, by following them, liking their posts, and viewing and liking their stories. That puts you in their notifications, they visit your profile, and a portion of them follow.
We unfollow after 4 days to keep your following count sensible, and we never touch anyone you followed yourself.
Then we watch what’s working. If some sources convert well and others don’t, we lean into the ones that do. If the followers coming in aren’t the right type, we rework the sources and try again. That loop is the actual strategy.