You are right, I don't want to remain ignorant. Educate us about the sudras and untouchables.
Brahmans, Kshatriyas, Vaisyas, and Sudras are the four Hindu castes. These castes or groupings are called varnas. Whatever caste or varna a baby is born into will be his or her varna for life. Marriages for young people are arranged within one's caste. Each caste has its codes of conduct and unique lifestyles. For example, upper caste members receive better education. For centuries lower caste members were forbidden to even acquire books. Sudras' work never allows them to gain financial independence or accumulate wealth. All wealth in Indian society is reserved for the top three castes.
Below the four varnas is a fifth group called Achuta, known as Untouchables.