Vaishya is the third varna in the varna-ashram system.
They serve as the economical backbone of the whole society, as they also maintain agriculture and protect the cows as said in Bhagvad Gita.
Bhagvad Gita 18.44
Krisi go raksya vanijyam
Vaisya karma svabhavajam
Paricaryatmakam karma m
Sudrasyapi svabhava jam
Translation- Agriculture, protection of the cows and business are prescribed work for the vaishyas, and for the sudras the dharma is labor and service to others (other varnas).
A vaishya shall also undergo upanayan samskar and study Veda and its anga(s) (parts), though all of the dvijas have the right to study the Veda only a Brahmin shall teach the Veda to the dvijas as it is their fundamental duty to teach as said in Manu smriti.
Manu smriti (Chapter 1, verse 88)
Adhyapanamadhyayanam- yajanam yaajanam tatha
Daanam pratigraham chaiva brahmananamkalpayat
Translation- for the Brahmins studying-teaching, doing yajna (worship through sacrificial fire of devatas) and making others do yajnas, accepting and giving donations, these 6 are the prescribed duties.