You can follow someone by finding them in your contacts, through Facebook, or through the suggestions in your feed. If that person's profile is set to private, they will need to accept your request to follow them. 

If your profile is set to private, you will need to approve any requests you receive from people who wish to follow you.

You can remove a follower by navigating to the My Profile tab by tapping on your name or photo from the home tab. A list of your followers will show underneath your name. Select the three dots to the right of the person's name and remove them. The person will not be notified of this action.