Hindu scriptures include:
4 Vedas
108 Upanishads
18 Puranas
the Ramayana
the Mahabharata (The Bhagavad Gita is a tiny part of the Mahabharata.)
Hinduism is polytheistic, with dozens of gods, but there are three major deities: Brahma, Vishnu, and Shiva, together called the Trimurti (meaning 'trinity'). Their respective consorts, Saraswati, Lakshmi, and Parvati, are collectively called Tridevi (meaning 'three goddesses').
Brahma is the Creator of the universe. He grants wishes to those who pray to him, even if they are demons. His consort is Saraswati (the Goddess of learning and music). The mischievous and humorous Sage Narada is the son of Brahma. Brahma and Saraswati reside in Brahmaloka. Brahma never fights; therefore, he wields no weapons. He has four heads (representing the four Vedas) and four arms. His mount (vehicle) is a swan.
Vishnu is the Preserver of the universe. He periodically incarnates on Earth to destroy the forces of evil. Some of his popular incarnations (avatars) are Lord Rama from the Ramayana and Lord Krishna from the Mahabharata. Vishnu's consort is Lakshmi (the Goddess of wealth and prosperity). Vishnu and Lakshmi lie on the body of a gigantic multi-headed serpent called Shesha in Vaikuntha (meaning 'place of eternal bliss'). Vishnu's weapon of choice is the Sudarshan Chakra—a fast-rotating disc with a sharp, serrated circumference—which he uses to decapitate demons. Vishnu has four arms; his mount (vehicle) is an eagle named Garuda, the king of the birds.
Shiva is the Destroyer of the universe; he will destroy the universe at the end of each 'cycle'. Parvati (the Goddess of energy and beauty) is his consort. He also sometimes incarnates on Earth, but his avatars are generally less prominent than Vishnu's. He has a third eye in the middle of his forehead, which emits fire when opened. Thankfully, he opens it only when infuriated. Shiva's most famous avatar is the monkey-god Hanuman from the Ramayana. Shiva and Parvati reside on the summit of Mount Kailash with their attendants. They have two children: Kartikeya and Ganesha. Shiva's weapon of choice is the Trident. A snake called Vasuki resides on Shiva's neck. Shiva's mount (vehicle) is the bull-god Nandi.
There are numerous less important gods and goddesses. Among them are:
Indra, the king of the gods, and his wife, Shachi
the Sun god
the Moon god
the Fire god
the Rain god
the Wind god
Brihaspati, the gods' guru
Vishvakarma, the divine architect
Kamadeva, the god of love, and his consort, Rati
Yamaraja, the god of death
Several apsaras (celestial nymphs)
Brahman - the supreme, formless reality
Brahmarshi - the highest class of sages
guru dakshina - payment for a guru's services
Maharshi - great sage
Rajarshi - royal sage
sati - the practice wherein a new widow is expected to kill herself by self-immolating on her husband's funeral pyre (This ghastly practice has long been abolished in India.)
swayamvara - a ritual where a bride chooses her groom from a group of suitors
yagya - any ritual done before a sacred fire
yojana - a traditional measure of distance, reckoned variously as between about 3.5 km and 15 km
Vaishnavism - Its adherents, who believe Lord Vishnu is the supreme being, are called Vaishnavites.
Shaivism - Its adherents, who believe Lord Shiva is supreme, are called Shaivites.
Shaktism - Its adherents, who believe that the supreme being is feminine, are called Shaktas. All goddesses are manifestations of this supreme feminine being called Goddess Shakti.
Smartism - Its adherents are called Smartas. They worship five deities—Shiva, Vishnu, Devi (Goddess), Sun god, and Ganesha—as manifestations of Brahman.
Hinduism has different castes or varnas:
Brahmins (Priests and Intellectuals)
Kshatriyas (Warriors)
Vaishyas (Merchants)
Shudras (Manual laborers and Artisans)
Dalits (Untouchables)
The caste system is one of the modern evils of Hinduism.