Hinduism defies attempts to define it in any specific sense. Some argue that it is more an association of religions. It has no founder, central authority or hierarchy.
It is not a proselytising religion. You can't be converted; to be a Hindu you must be born one. The strictly orthodox maintain that only a person born in India of Hindu parents can truly claim to be Hindu. To outsiders Hinduism often appears as a complex mix of contradictory beliefs and multiple gods. In theory it happily incorporates all forms of belief and worship. But for Hindus religious truth is ineffable; at its heart, Hinduism does not depend on the belief in the existence or other wise of any individual or multiple gods.
Essentially, all Hindus believe in Brahman, the One without a second, without attributes. Brahman is eternal, uncreated and infinite; everything that exists emanates from Brahman and will ultimately return to it. The multitude of gods and goddesses are merely manifestations knowable aspects of this formless phenomenon - and one may freely pick and choose among them. Although beliefs and practices vary widely from region to region, there are several unifying factors. These include common beliefs in reincarnation, karma (conduct or action) and dharma (appropriate behaviour for one's station in life), and in the caste system (see Society & Conduct in the Facts about India chapter). Hindus believe earthly life is cyclical; you are born again and again (a process known as samsara), the quality of these rebirths being dependent upon your karma in previous lives. There is no escaping your behaviour. Living a dharmic life and fulfilling your duty will enhance your chances of being born into a higher caste and better circumstances. Going the other way, rebirth may take animal form, but it's only as a human that you will gain sufficient self-knowledge to escape the cycle of reincarnation and achieve moksha (liberation). Traditionally, women are unable to attain moksha. The best they can do is fulfill their dharma and hope for a male incarnation next time round. For ordinary Hindus, fulfilling one's ritual and social duties is the main aim of worldly life. The Bhagavad Gita (see Sacred Texts later) is clear about this; doing your duty is more important than asserting your rights.
That the householder and the renunciate may equally earn religious merit is a notion that was enshrined some 2000 years ago in the Brahmanic ashrama system. This kind of merit is only available to the upper three castes. Essentially there are three stages in life recognised under the ashrama system: brahmachari, or chaste student; grahastha, the householder; who discharges their duty to their ancestors by having sons and making sacrifices to the gods; and sanyasin, the wandering ascetic who has renounced worldly things. The disinterested discharge of your ritual and social obligations is known as karma-marga and is one path to salvation.
But there are others, including jnana-marga, or the way of knowledge (the study and practise of yoga and meditation), and bhakti-marga, devotion to a personal god. The latter path is open to women and shudras (caste of labourers).