What do Hinduism people believe in?

You have asked a very ambiguous question. The question should have been, 'what Hinduism people do not believe in'? The answer would have been that there is nothing that hindus do not believe in. Which is what happens when you give the right to hold individual opinions to a billion people. No two hindus have exactly the same kind of belief. There are all kinds of beliefs in Hinduism, right from polytheism to monotheism to monism to atheism. They believe in science, they believe in voo-doo also, in ghosts and angels. Hindu belief cannot in any way be limited.
The answer to 'what Hinduism people believe in?' is social responsibilities and peace, or 'Dharma' (duty and righteous action). The main concern of Hinduism is that the family should lead a satisfied, peaceful, and progressive life; and there should be no discord in the society.