What is Upakarma?
Upakarma is a Sanskrit word (Upa + Karma). Literally Upa means before and Karma means an action. Upakarma means an action performed before beginning the Vedic studies. Upa also refers to nearness or close touch with Upanishads (Vedas). In simple terms Upakarma refers to changing of sacred thread called Yagnopaveetham on this day by the three varnas (Brahmins, Kshatriyas and Vysyas).
Why do we celebrate?
Upakarma means beginning,to begin the study of the Veda. Why begin study of the Vedas on this particular day? This auspicious day also happens to be the day when Lord Narayana took the avatara as Lord Hayagriva. Lord Hayagriva as we all know restored the Vedas to Brahma and also is the God of Knowledge.
What should we do?
After taking holy bath, one has to wear new Yagnopaveetham (both married and unmarried) with proper sankalpa and invocation.
Perform Gayathri Japa (according to one’s capacity, at least #108 times)
At temples and Mutts where this event is performed collectively, Homa is also performed.
As a symbolic commencement of study of Vedas one can recite Purusha Sooktha and Sri Vishnu Sahasra Nama Sthothram on this day.