India is the home of Philosophy, Religion and Spirituality. Every age, she provides the world with her armies of spiritual masters. She uses every means to reach the people of various parts of the world to enlighten them to the grand avenues of a meaningful life. The world wide web is no exception. There are several sites which give very indepth information of the various concepts and various schools of Indian Religion.
Here are a few sites which give general information on religions of direct Indian origin. (More specific links follow in the course of this article.)
In India, spirituality is basically tuning one's mind to consider one's self and others as different from the gross physical body and the subtle mental body, and to be beyond the limitations of space, time and causation. Philosophy is the theory aspect and religion is the practical aspect of this principle.
The beauty of the Indian philosophy is the grand unification of a Metaphysical God who is the Absolute Reality and the substratum of all existence, and a Personal God who is the basis of all morality, ethics and the inspiration to lead a meaningful life. This grand unification makes the Indian religious temper one of the most tolerant and all consuming of the religions, and also the mother of many religions of the world today.
The Indian religious temper, called Hinduism, is more ancient than the oldest known Rig Vedic hymn, which is dated to about 5000 BC, and yet is as modern as the school of thought sprung yesterday. This dynamic nature of the religion, based on a firm foundation makes it one of the most sagacious and vibrant of religions.
Here are a few articles which give the fundamental concepts of Indian religions in general and Hinduism in particular.
Here is an FAQ on Hinduism, which may answer most of your questions.
Hinduism was not originated by any person. Its fundamental principles are accepted by the Indian people from time immemorial. Several spiritual teachers have put down in words their thoughts about the concepts and their perception of spiritual life based on these concepts. These serve as guiding lights for several generations of the future.
The books of Hinduism are classified into two catagories, namely, Srutis and Smritis. Srutis are mere records of the fundamental principles of spiritual life and the experiences of spiritual giants. They do not try to fit their experiences into any model to explain them. They are just a statement of facts. This makes them totally impersonal and independant of the cultural and intellectual background of their authors. For this reason, Hinduism which is based on these texts as the foundation is known by the name Sanathana Dharma -- the eternal way. These texts are the Vedas. The portions of the Vedas which describe the principles of spiritual life are the Upanisads. Though there are innumerable Upanisads, all the concepts explained in them can be found in 10 of them, for which Sri Sankara, one of the brightest stars in the Indian spiritual sky, has written explanatory notes. All the other Upanisads put the same concepts covered in these, in different words.
The Smritis are also written by great authorities in this field. These propose models of God, Man and the Universe to fit into the general principles laid down by the Srutis. These are coloured by the cultural background of the author, and so cannot be taken at their face value for an age, place and cultural background different from those for which they were originally written.
Here are a few texts which are considered authoritative. Their translations may not be authoritative. So, one has to be very careful while going through such translations.
As mentioned before, Hinduism allows various schools of thought under its broad principles. This has resulted in innumerable sects and cults. Some of them stay active for hundreds of years, while some form and vanish like bubbles. Most of them get merged into other existing sects, thus strengthening them.
Here are a few long living schools which are a few centuries, and some of them even a few millenia old.
Here are a few schools which have come up within the past one or two centuries.
The Indian view is to see all religions as various ways to reach the same goal of manifesting the intrinsic divinity in man. So a follower of the Indian spiritual tradition accepts all religions to be true and suited for people with various mental structures, if followed in the right spirit. This was explicitly demonstrated by Sri Ramakrishna (1836-1886) in his life. He took up various religions and spiritual paths like Vaishnavism, Shaaktha, Advaitism, Christianity and Islam, one after the other, one at a time, followed them in full ernest and showed that they all lead to the same goal.
Here are a few links to religious traditions, not directly of Indian origin.