The Upanishads state that the only way for the atman to get back where it belongs is through samsara, or reincarnation. The person's atman (soul) may begin as a worm, then through death and rebirth it goes higher and higher in the order of things until it becomes a human being. Once the atman becomes a real human body, it must progress by attaining higher social classes. The human being attains a higher social class by folowing his dharma - his duty to certain things according to the class he is in. These things include moral, social and religious duties - they are vitally important to the Hindu.
Another way to release the soul is through yoga, a discipline that holds one's physical passions in check so that the atman can escape the cycle of death and rebirth and be joined with the paramatman (world soul).
Once the atmas has lost itself and its identity in paramatman, or the true reality, it is said to have passed into moksha (the infinite). Then and only then is the school of life over for the Hindu. He graduates into the infinite.