The Brahmins were the descendents of Indo-Europeans, and they established the caste system. It isn't based around "class" exactly, because back in Vedic India caste was class. Think of it like your slavery days, a black person was a slave, while a white person could be anything.
Brahmins served as priests and interpreted religious texts, for over a few millennium only they had the right to learn Sanskrit. Kshatriyas were divided into various groups, Rajputs served as the royalty as well as warriors and soldiers, Kayastha served as the nobility and took care of recording taxes.
Vaishyas were businessmen and artisans, they served as sculptors who were commissioned by the royalty to construct various monuments and sculptures.
Shudras were the lowest caste, their job was usually cleaning and collecting trash. They weren't considered untouchable so they were employed in palaces, or worked as people who washed clothes etc..
Dalits and tribal people were considered "untouchable", meaning that they were not present in the varna system.
Just see how the Vedas calls the "caste" system as "varna" system. "Varna" in Sanskrit means "colour".
Even today, certain castes have large amounts of Indo-European DNA, all Brahmin castes average about 17% of Yamnya DNA, while certain castes like Haryanvi Jatt have almost 30% Indo-European DNA. The most common Haplotype among the upper castes is R1a1, while in the lower castes (and non-Brahmin Southern Indians) is J.
Tamil Brahmins speak a Dravidian language, but the interesting part is that the Tamil they speak is filled with Sanskrit words, and so is modern Tamil.