Points on Realms refers to where your realm is ranked. When someone /like s your realm their like power is added to your total Points. These points reflect where your position is in top realms and how many stars your realm has.

Reputation are the points you get from placing blocks on the server. The amount of points you get can be found from typing /rep ingame. These points relate to your rank on the server and with enough Reputation you can rank on the server.

Clear enough now?