The Rh factor identifies whether your blood is type positive or type negative. If you are Rh+, you carry the Rh antigen. If you are Rh-, you do not carry the antigen. If a person who is Rh- receives blood that is positive, then they will form anti-Rh+ antibodies to destroy the foreign blood.
The relationship to the Rhesus monkey is that these antigens were first discovered in the blood from a Rhesus monkey and then later discovered in human blood.