Some people have reached the total number of friends they can have which is 5000. Such people can no longer send or accept friend requests on Facebook. This made Facebook bring out the follow option which means you can follow someone without being a friend with the person.
When you follow a profile on Facebook you will be able to see their posts on Facebook and whatever updates they have.
How to follow someone on Facebook
Go to the person’s profile and click on Follow. Things have changed a bit, you might not be able to see the follow button because the person has changed it from his settings because he doesn’t want to be followed. The simple thing you can do is to send him a friend request, once you do that you automatically follow (if the person allows that from his Facebook settings) that profile even though your request hasn’t been confirmed.