@PartialGestalt Follow is as usual that everybody knows. They get notified that you're following them. You can read their follower-only posts. And in case they curate their followers, you would have to apply for following and they'd have to approve it first.

Subscribe allows you to 'follow' without needing approval/permission and without informing them. The only thing is that you only get to see their public toots as it's not a real follow, just a way for you to keep up with their public postings.