Hindu is a term given by Britishers for the people of India.Technically there's no religion like a Hindu but it is now used to collectively refer to people who follow the Ancinet India Religion which is called as Vedic Religion.Over the centuries many sects have come up among the people who followed Vedic Religion.Hindu refers to any person who follow Vedic Religion or any sect which is a subset of Vedic Religion.
Coming to your original question,Brahmin is one among four classes defined in Vedic Religion.Other 3 being the Kshatriyas ( Warrior Class), the Vaishyas ( Trader/Business Class), and the Shudras( that performs the lowest level of work).Brahmins are the highest class as they are supposed to be direct descendant of God and one that is known to posses intellectual wealth and considered the protector of Vedic Traditions.