What are the main differences in theravada and mahayana buddhism?
The main difference I'm aware of is that the Therevada school is focused on seeking Enlightenment for the individual. The Mahayana school is focused on seeking Enlightenment for the sake of all sentient beings.
If I remember correctly, for those who believe in the literal Western interpretation of reincarnation, according to the Therevada school, when someone attains Enlightenment they will cease worldly rebirth. Alternatively, the Mahayana school believes that a fully-awakened buddha can choose to be reborn, and even choose their rebirths.
From my understanding, there are a lot of other differences--many of them relating to monastic life.