Facebook is complicated. There are two kinds of connections that you can have with people on Facebook: friends, who are people you’ve explicitly friended on Facebook, and followers, who may be complete strangers.

Friends are always followers, but if you make posts public then it’s possible for non-friends to follow you too – and if you ignore or delete friend requests, those people automatically become followers who can see your public posts.

To see who’s following you, go to your profile page and click 'Friends'. If you’ve made it possible for people to follow you you’ll see a 'Followers' link; if you haven’t, you won’t.

Most followers are just interested in what you’re posting, but if you fear that someone’s following you for more sinister reasons then it’s possible to block individual people without disabling the following feature altogether. To do that, go to the account settings page and look for 'Blocking' (it’s just below 'Privacy'). This enables you to block people altogether, to restrict specific contacts from seeing friends-only posts, or to block messages or apps either on a per-app or per-person-who-keeps-sending-you-invites basis. You can also block people from contacting you via Facebook Messenger.

http://www.techmej.com/2017/09/see-whos-following-you-on-facebook.html

So much text for one easy thing to check