theravada - you get yourself to Nirvana. For instance people who are not monks/nuns cannot reach Nirvana. The road to extinction is a long one, you have to be reincarnated several times to reach the status of arhat as a munk.

mahayana - you can get help to get to Nirvana. Even ordinary people can achieve "bliss"/extinction. Buddha did not enter Nirvana at once when he achieved it, from that the mahayana has learnt that when you do reach the goal, you stay and lead others, become a bodhisattva! They also have a place somewhat like heaven! Often called the Western Paradise, which was created by the one buddha; Amithaba Buddha. Actually all other Buddhas and Bodhisattvas are revelations of this ONE Buddha.

The name mahayana means the Greater Vehicle. The mahayana school often refer to the Theravada as hinayana, the Small Vehicle; this because they think the hinayana followers are selfish and only mind their own "bliss".