What do you call someone that believes in Hinduism?

Answer 1

A person who follows the Hinduism religion is called a Hindu. There are Hindus all around the world. You need not be an Indian to be an Hindu. That is a common misconception. There is no converting to Hinduism, you just start practising it and following it. Just like Buddhism and Confucianism.

Answer 2

The person leading any given Sanatan Dharma (Hindu Religion) ceremony is classed as a Brahman. The follower or more precisely, the one or taking down the instructions and acting upon such commands is known as Yajmaan. The peopleattending such ceremony are known as Shrota or Shrotajan. Please note that Shrota translated could be construed to mean a spectator but here, the term Shrota is more subtle and means a ceremonial follower. Shrotajan is purely a plural term used for respected attendees.