The caste system is a is a system that determines what social status. When you are born into a certain caste, you stay in that caste and you can only communicate with those in you caste. If a person in a higher caste interacts with one in a lower caste, it is seen as shameful.
It is believed that the first ideas of the caste system came from the ancient Aryans when they invaded South Asia. When they invaded India they used the caste system to control the local populations. Since then, India has used the caste system.
Although the caste system is illegal, many people still categorize people using it in their daily lives. The people in higher castes treat the Dalit's like trash making them do jobs that they don't want to. These jobs include cleaning public toilets and sewage work. People in higher castes can become office workers and teachers just because of their caste.
Even with the caste system being illegal, people are still resorting to violence to keep it form disappearing. There have been attacks on the Dalits because they are seen as inferior to everyone else.