Describe the central tenets of Jainism, Buddhism and Hinduism. What similarities can be found among these three religions?
It would be quite presumptuous to think I could do full justice to the details of three major world religions in a single post, but I think I can at least give you some of the broad strokes about their similarities and differences.
All three religions are found primarily in India and East Asia, and have existed for at least 2000 years. All three are very complex and have a variety of different traditions---especially Hinduism, which is probably the most diverse religion in the world. All three religions share the common basic moral values that are found in almost every human culture, such as prohibitions on murder, theft, and fraud. All three religions involve belief in reincarnation and karma in at least some of their sects. In addition, all three religions emphasize meditation and nonviolence as paths to enlightenment.
Jainism takes nonviolence particularly seriously, as many Jain are strict vegans who believe that all living things have souls, and seek to minimize their harmful impact on all things, even the plants and the soil. Buddhists and Hindus are also often vegetarians, but a significant number are not.
Sexuality is viewed quite differently in Hinduism compared to the other two religions; there is a strong tradition of Hinduism viewing sexuality as an important part of enlightenment (such as the Kama Sutra, which is actually a Hindu sacred text as well as a sex manual). Buddhism and Jainism generally view sexuality as a form of personal indulgence that is to be generally minimized if not avoided altogether. Due to the great diversity of beliefs within these religions, there are many exceptions to both of these broad patterns.
Buddhism and Jainism are both more codified than Hinduism.
Hinduism has no one particular text or set of laws that all Hindus believe in.
Almost all Buddhists follow the Three Practices (virtue, meditation, enlightenment) and the Four Noble Truths (suffering exists, suffering is caused, suffering can be ended, suffering is ended by following the eightfold path).
Almost all Jain believe in the Three Jewels (right belief, right knowledge, right conduct), as well as the Five Great Vows.
Then we come to the thorny question of how many gods. Buddhists may believe in no god, one god, or many gods. Hindus generally believe in many gods, but often have one god that they believe all other gods come from. Jain generally believe in no gods at all.