Once upon a time, long long ago, Surya, the sun God, was married to a beautiful princess called Samjna (also prounced as Sangya). In course of a year, she presented Him with twins.
The twins were christened Yama, and Varni or Yamuna, and they grew up together.
However, Samjna, after some time, were unable to bear the brilliance of her husband, decided to go back to earth. However, she left her shadow, Chaya, her exact replica, behind, so that to Surya, it would appear that she is still there.

In course of time, Chhaya turned out to be a cruel stepmother and was very unkind to the twins. She soon gave birth to her own children, and at that time convinced Surya to drive out Samjna’s twins, Yama and Varni from the heaven. Varni fell to earth and became the river Yamuna, and Yama went to the underworld (hell) and became the King of Death!

Years passed. Varni married a handsome prince and was content and happy in her life. But she missed her brother and yearned to see him. Yama, too, missed his sister and decided one day to visit her.

Overjoyed by news of her brother's visit, Varni prepared a great feast in his honor. It was two days into Deepavali, so her home was already decorated with pretty lamps. She lovingly prepared a feast, including all the sweets and delicacies that her brother loved. Her husband, the handsome prince, was very happy seeing Varni so dedicatedly preparing a welcome for her brother.

Yama, too, was delighted by his sister's loving welcome, and brother and sister spent a pleasant evening in each other's company, after their long period of separation.

When it was time for Yama to return to his kingdom in hell, he turned to his sister and said, "Dear Varni, you have welcomed me so lovingly. But I did not bring you a gift. Ask, therefore, for something and it will be yours."

"Your visit is gift enough," replied Varni lovingly. "I have no need of anything else."

But Yama was persistent. "You must let me give you a gift," he insisted.

"Okay," agreed Varni, taking a moment to think. "I ask that all brothers should remember their sisters on this day and visit them if they can, and that, on this day, all sisters should pray for the happiness of their brothers."
"So be it!" proclaimed Yama, the King of Death, adding, "And I grant all brothers who give their sisters a loving gift on this day a long and healthy life!"
And this is how the custom of Bhai-duj, or bhai-phonta, came into practice. Bhai duj is celebrated widely across India, when sisters give a tika or phonta, (a mark or bindiya with the help of the finger dipped in sandal or curd) on the forehead of their brothers.
So traditionally all brothers visit their sisters on this day, exchange good feelings, and give them loving gifts. Sisters too, pray for their brohers lng life nd good health, and general well-being.

So, to all you brothers out there: Be sure to remember your sisters on this day and give them loving gifts-be they ever so small.

And, to all sisters: You, too, must think of your brothers and pray for their well-being on this special day.