Theravada Buddhism is also known as Southern Buddhism. It is about 2000 years old, as is Mahayana Buddhism. It focuses on the detachment of the individual from the personal self, and thus working to come closer to nirvana. This detachment takes the form of reducing desire and therefore suffering.
It is more uniform than is Mahayana Buddhism, having fewer sects. Theravada Buddhism is also usually studied in the Pali language, while Mahayana Buddhism is not so picky.
See the Four Noble Truths and specifically The Eightfold Path for instructions on how to reduce desire.
See also: Karma
And compare to Mahayana.