we have this fan page built in google+ then there's a + button and there's the follow button. now question is how do this two differ in a sense bought are in the google+ features?
I don't understand your question exactly..... The + button is a like kind of button, When you do +1, it adds value to the post. When you follow someone, you will be seeing all the posts shared by that person on your wall.
In Google+, + is similar to the Facebook Like but it is more powerful than Like. + use to up your vote and, value of the post and follow button is similar to Twitter follow button you can follow your interests or follow a person to get updates from him............
Same as facebook in facebook you can like or subscribe, google has plus 1 which = like plus they have follow
Obviously Google + have you heard a proverb "charity begins at home" What ever you will post on Google + will come in eye of robot first than any other place in this internet world. because of this benefit Google + is gaining this much traffic. I have seen blogs who have few likes but 100+ google + and they are top in Google rankings.