All societies have some sort of social class system in which people are classified based on education, culture, and income levels. In ancient India, such a system was inspired by Hindu scriptures and implemented as a way to create a society in which all essential functions were addressed and all people assumed vital roles based on their abilities.
Centuries later, the classification was dubbed the caste system. While the caste system in practice became seriously flawed, its concept was based on this ideal division:
Brahmin: The priestly/intellectual class
The ideal brahmin has qualities of serenity, self-restraint, purity, forgiveness, uprightness, knowledge, realization, and belief in God. The associated “job description” includes
Serving as a gatekeeper of knowledge of Brahman
Providing intellectual advice to governing bodies
Offering priestly services and religious leadership
Grappling with fundamental questions of life
Kshatriyas: The warrior class
The requisite talents for kshatriyas are physical prowess, courage, splendor, firmness, dexterity, stalwartness in battle, generosity, and lordliness. The associated functions include
Defending the country from external aggression or internal strife
Specializing in the science of arms, ammunition, strategies, and tactics of warfare
Vaishyas: The trade/commerce class
The vaishyas specialize in trade and commerce in order to procure goods and services so that the society as a whole can lead a life of plenty. Modern vaishyas are primarily traders and entrepreneurs. No specific qualities are prescribed in the Hindu scriptures for this and the next caste.
Shudras: The agricultural/labor class
The shudras do manual labor such as tilling the land, working in the fields, and raising cattle and crops. In practice, this caste came to include everyone not belonging to the other three castes, except for the untouchables: people performing the most menial labor, such as sweeping streets and tanning leather.
Note that the creation of a group called untouchables was a manmade perversion of the caste concept set forth in Hindu scripture — a perversion fought by modern Indian leaders such as Mahatma Gandhi.