Friends differ from followers by way of how much access they have to your content and your profile. You can follow anyone on Facebook, but this does not necessarily make them your friend. They only become your friend if you submit a friend request and they accept it.
With Facebook friends, you both see each other's posts. When you follow someone on Facebook, you see their content, but they don't see yours. Following is a one-way relationship, whereas friendship is a two-way relationship.