As the Bhagavata tells it
Bhagavata Purana 3.8 to 3.10 · 3 min read
At the end of an age the worlds had gone back into the water, and there was nothing but the dark ocean. Vishnu lay on it asleep, on the coils of the serpent Shesha, with all the worlds folded up inside him.
When the time came for the worlds to be made again, a lotus stalk began to grow from his navel. It rose up out of the water and opened into a great lotus, bright as a thousand suns, and in the middle of the lotus sat Brahma.
Brahma looked around him. There was nothing to see, only water in every direction, and the dark. He did not know who he was, or where he had come from, or why he was there.
"Who am I?" he said. "And what is this lotus I am sitting on? Something must hold it up."
He climbed down into the stalk of the lotus and followed it down through the water, looking for its root. He went down for a hundred years and never reached the bottom. At last he gave up, climbed back to his seat on the lotus, and sat there, lost.
Then out of the water he heard a voice, saying two syllables twice over. "Tapa. Tapa." It meant: practise austerity.
Brahma did not see who had spoken, but he obeyed. He sat still on the lotus, held his breath and turned his mind inward, and he stayed that way for a thousand years of the gods.
When he had done it, Vishnu showed himself. Brahma saw him lying on the serpent in the water, dark and shining, wearing yellow silk and garlands of forest flowers, with the lotus rising out of his own body and Brahma on it.
Brahma bowed his four heads and praised him. "I know now where I came from," he said. "Tell me what I am for."
"You are for making the worlds," said Vishnu. "Do it as you have done it in the ages before, and do not be afraid. Everything you need is already in you. When you are troubled, think of me."
Then Vishnu was gone, and Brahma was alone again on the lotus, but he was no longer lost. He divided the lotus into the three worlds, earth, sky and heaven. He made time, and then out of his mind he made the sages, and the gods and demons, and the people, and the animals and the plants, all in their order.
The tellers of the south and the Deccan say that the first thing he made was time, and that he began it at a sunrise. The almanacs quote a verse to say which one: in the month of Chaitra, on the first day of the bright half, at the moment the sun rose, Brahma made the world.
That is why the year begins on that morning. Before dawn on Ugadi people bathe with oil, put on new clothes and hang mango leaves over the door. They eat a mixture of six tastes, sweet and bitter, sour and salty, hot and astringent, for the whole year that is coming. And in the evening they sit before a priest who reads from the new almanac, the panchanga, what the year that Brahma began on that morning holds for them.