How is Rakshabandhan celebrated according to Vedic Scriptures?
Rakshabandhan is not just a festival that celebrates the love between brothers and sisters; it has much greater significance too.

In present times, Raksha Bandhan is perceived in a limited and manufactured way. The sister ties the Raksha Sutra to her brother, who, in turn, assures her of protection. And, as a gesture of love, he gives her gifts. However, when we go deeper into the sources of this tradition, this custom has been prevalent only in the last 500-600 years. In reality, very few people are aware of the origins of Raksha Bandhan.
What Puranas say about Rakhi? Is Rakshabandhan just a festival about sisters tying rakhis to their brothers?
Raksha Bandhan is an auspicious festival for those tying the Raksha Sutra. In ancient times, when Vedic traditions were widespread, gurus used to tie the Raksha Sutra to their disciples on the Purnima day of Shravan. The Raksha Sutra was the Vedic initiation to start studying the Vedas. The guru, by tying the Raksha Sutra, would signal his acceptance of the disciple. The disciple, in turn, would resolve to start his journey of studies in the tutelage of his guru and serve him. This Vedic tradition is explained in Narad Purana. ( Narad Puran - Poorv Bhag - Chaturth Paad)
In the 137th chapter of Bhavishya Purana, when King Yudhisthir asked Lord Sri Krishna, the Lord explained the Vedic history of Raksha Bandhan and the reason why is it celebrated with such joyfulness. In this context, the Lord said that Indra’s wife, Sachi Devi, had tied the Raksha Sutra to her husband, the king of gods before he set out for battle in the epic fight between the devas and asuras. Because of the powers of this Sutra, Indra remained protected in the frightful struggle and was able to defeat the asuras.
It is clear that this festival is not just about sisters tying rakhis to their brothers; it is of far greater significance.