NOTE: Urban Hindu follow either Vaishnavaism (Vishnu as the ultimate deity) or Shivaism (Shiva as the ultimate deity). As you will see, neither of these concepts really matter in the scope of HINDUISM. Rural Hindu worship their own village goddess. Think of a Thai village where villagers might worship a manifestation of Buddha known as Ong-Bak. In terms of gaming, this is an incredible interpretation of god that GMs and players can use to great effect.
Hinduism supports the belief of numerous gods, sometimes called henotheism, but names only a few (respectively of the 36 trillion manifestations of Ganesh). Most Hindus believe in the ātman (eternal soul) — the true "self" of every person, which is difficult to distinguish from the Braham, the supreme spirit (based on ancient traditions of Vedic mythology). This concept is similar to Buddhist enlightenment, perhaps stealing from one another over the centuries, as an individual attempts to bring his ātman and Braham into alignment, so he might "ascend" (cf. moksha)
Hindu believe in avatars and deva, which fits well with D&D pathos. Like Catholics turning to the Saints for blessings, Hindu seek blessings from Deva. Since they also seek the awareness of God in everything around them (more on this later), one is always contemplating divinity "in the midst of everyday life."
When using Hinduism in an RPG, it's important to note that symbolism and iconography are rampant in the culture/religion, lending to blessing (Om, for instance) everywhere you turn. Using this concept (but not these exact symbols) works well with how gamers perceive their character's religious convictions. Chanting, meditation, and yoga are also fundamental ways of channeling praise/prayers and put Hindu on the course of spiritual "rightness."
God (lower and upper case)
When considering GOD in Hinduism, it is important to note that dependent upon the manner in which he/she is evokes, determines the name he/she is given. This is extremely difficult for westerners and students of traditional mythologies. Names such as Advaita, Bhagavan, Parameshwara, Brahma, Ganesh, Ganesha, Ishvara, Ishwar, Krishna, Rama, Shiv, Shiva, Shakti, and Vishnu can all be used by various sects to define god and the various manifestation he may project. Add to this that there are ten avatars of Vishnu, and nine Navagrahams (manifestations of Bhagavan connected to the planets and the days of the week) the head begins to swim.
The main Hindu bible (and there are many) is called the Bhagvadgita (I've read parts of it, but man…). Here, I'll let someone else explain it.
For those who do not know the long and the short of it in Mahabharata -it is the before and after of an epic war between the Pandavas (or children who took Pandu's name though born out of the gods), and Kauravas - the evil ones try to usurp other's property by foul means. In the end there is a major war, which leaves millions dead, but Pandavas emerge victorious.But beyond this key tome lies the Shruti and Smritis (that which is heard, that which is known, respectively). The Shruti are four Vedas (and those are all named), the earliest Hindu scriptures. The Smritis are epics (of which there are many, though two key ones). The Bhagvadgita is one of these epics. Confused yet?
In Hinduism there is no concept of evil, which means that demons and the like don't really fit into the paradigm. There is a hell, however, named Naraka. Rules by Dharma Raja (literally King of Dharma) who rules as the god of righteousness (another manifestation). However, one does not suffer in hell forever, but rather waits to enter heaven (Swarga). Additionally, if the soul must atone for Kharma and has not reached Moksha (salvation), then it returns to continue the cycle.
Every being is good, according to Hinduism. Made this way by Brahma. But sometimes people adopt bad ways. This may or may not be under their control. But the Kharmic wheel assures that this cannot last forever.
The Big One
Hinduism has no real begining. No one can say for sure when it started, where it began. It has no founder and no core doctrine. [Yes, there's Smriti that teach values and beliefs, but this bible does not offer answers or resolutions to disputes.] It does not require dogmatic adherence. It is cultural, not creedal. The Absolute “Brahman” cannot be equated with “God” in the Western sense of religion. This concept is exclusive to Hinduism (if we accept that Buddhism is not a religion, but a way of life).
Hinduism is so diverse, it defies easy categorization. Hinduism accommodates perspectives other than its own. It is characterized by a tapestry of ideals, concepts, variations, and practices resulting in an amalgam known as Hinduism. Essentially, it is an umbrella religion, holding many independent ideals.
Hinduism is also highly tolerant of other religions.
Ekam Sataha Vipraha Bahudha Vadanti
"The truth is One, but different Sages call it by Different Names"