Your friends automatically follow you. You can also let people who aren't your friends follow you.

Click Public Posts on the left.
Select Friends or Public next to Who Can Follow Me.
See Who's Following YouIf you've allowed people to follow you, you can see a list of your followers by going to your profile, clicking Friends below your cover photo and then clicking Followers. If you don't have any followers, you won't see this option.
If you let people who aren't your friends follow you, people who send friend requests that you ignore or delete will automatically start following you. If you don't want someone to follow you, you can block them at any time.