Theravada, or “teachings of the elders” in Pali, is the oldest school of Buddhism. Main teachings of Theravada Buddhism are based on the earliest teachings of Lord Buddha’s (the Tripitaka or Pali Canon). Originally Theravada Buddhism was established in India. Although Theravada Buddhism is not a mainstream religion in India at present day, it is the main religion in the South East countries such as Thailand, Myanmar, Burma, Cambodia, Laos and Sri Lanka.
A comprehensive description of Theravada Buddhism can be found in http://www.accesstoinsight.org/lib/authors/bullitt/theravada.html