It is the school of Buddhism that believed it is the closest to the original teachings of the Buddha, hence the name “way of the elders”. The beliefs include that there is no omnipotent creator God, of the sort found in Judaism, Christianity and Islam. They believe that the truth of reality has been revealed in the person of Siddhartha Gautama “the awakened one” who understood the realities of suffering and how to minimise the pain of life. Finally, Theravada Buddhists believe the teachings of the Buddha can help us to achieve Nirvana.
The texts of Theravada Buddhism were written in about 300 BC and are now known as the Tipitaka - the three Pitakas. They are written in Pali, and contain codes for monastic life, the teachings of the Buddha and other philosophical ideas. They are often learnt by heart by Monks and nuns and certainly would have originally been fully memorised by groups of Monks rather than written down.
There are of course other denominations of Buddhism such as Mahayana BUddhism, Zen, Tibetan and Pure Land, but you will have to wait for those...