The reason questions regarding Judaism, Islam and Christianity are answered very quickly, but questions regarding Hinduism are only grudgingly answered, is because Hinduism is very complicated and difficult to explain relative to the three major monotheistic faiths.
Hinduism is practiced mainly in India, a country of over one billion people, although several hundred million of those are Muslims. Hinduism's origins go back more than 4,000 years, and are difficult to trace. The holiest text in Hinduism is the Rig Veda, which is believed to have been written more than six thousand years ago. While Hindus believe very strongly in reincarnation, and believe in a god who manifests itself in multiple incarnations. That God, Vishnu, also known as Brahma, is believed to be the creator of the universe and of all life on Earth. Vishnu, according to the theology of Hinduism, appears on Earth from time to time to vanquish evil, and to restore the Hindu way of life, or Dharma, which constitutes the laws, traditions, beliefs, and rituals under which followers live. Hinduism is not a monotheistic religion because Vishnu, while enjoying Supremacy, is only one of the gods to which Hindus worship, the others including Rama, Lakshmi, and Shiva, among many others. It is important to understand that some texts indicate that Vishnu and Brahma are the same god, and some indicate that they are different gods. Identifying gods to whom Hindus worship is, in fact, one of the major challenges of understanding Hinduism. The fact that Hindus believe God assumes infinite forms adds to the complications.
One commonly accepted notion of God in Hinduism is as follows:
Brahma is the Creator; Vishnu is the Preserver; and Shiva is the Destroyer. But, this is all subject to many alternative explanations.
Unlike God as worshipped by the three major monotheistic religions, Vishnu is given concrete form in Hindu texts, and is described as having four arms and the blue color of water-filled clouds, with a lotus flower in one hand, a mace in another, a conch in another, and a weapon called Sudarshana Chakra in the fourth hand. While the Old Testament (Genesis 1:1) describes man as having been formed in God's image, that is far more subject to interpretation than the physical description provided for Vishnu.
Unlike God as understood by Jews and Christians, the Supreme God in Hindu beliefs cannot be known, but is omnipresent. As stated, Hindus believe in reincarnation, which continues until a certain state is achieved and one is finally liberated from that cycle.
There are no formally defined characteristics of Hindu religion. Also there is no formal requirement for a person to qualify as a Hindu. Hinduism is a name give to the religion which has come down to the present age from the concepts and practices of original residents of the Indian sub-continent. A person becomes a Hindu in two ways. One by being born in a Hindu family, and second by practicing some of the ways associated with Hinduism.
I must clarify that there are no fixed practices or beliefs associated with Hinduism. Hinduism has multiple sets of belief, practices and deities, which are all loosely defined. Also these different beliefs, practices and deities are not associated with different sects of Hinduism. A Hindu may practice a religion that is a mix of these different sets.
Also a Hindu, particularly from India does not necessarily consider some major religions such as Sikhism and Jainism as different religions. Hindus, have no hesitation in visiting and praying at at their places of worship (like temples and gurudwaras). Similarly people belonging to these faiths have no hesitation in praying at Hindu Temples. People of these religions have many religious festivals and practices in common. In many families, different members may follow different religions. For example, in many families the eldest son become a Sikh while other siblings remain Hindu. Typically, marriages between Jains and non-Jain Hindus is common, and a girl readily and almost naturally gets cast in the religious ways of her husband.
However one essential aspect of Hindu religion, including its offshoots like Sikhism and Jainism are belief in the concept of Mukti as the ultimate goal and ultimate good of all beings. This Mukti may be simply described as release from the cycle of death and rebirth. Associated with this is the concept of Brahm, which is some kind of nothingness, and into which souls merge upon Mukti.
There are many different versions of the nature of mukti, the Brahma, and many alternate paths or ways of attaining mukti. A typical Hindu is not likely to have clear understanding of any one of these alternate versions. But almost every Hindus has some idea about it, chances are that his thinking and his actions are influenced by these concept, even if the person is not conscious of such influence.
It is important to note that none of the many social beliefs and religious rituals associated with Hindus and Hinduism are not essential part of Hinduism. As a matter of fact many authentic religious texts of Hinduism emphasize that following of rituals and adherence to rigid social customs is infinitely inferior to sincere action carried out with firm commitment to truth and service to others.