Her birth
Radha was born to King Vrishabhanu and Queen Kirti. One story says Vrishabhanu found her on a lotus in a pond, radiant as gold. Another says she kept her eyes closed after birth and opened them only when the infant Krishna was brought before her, so that the first face she saw would be his. She grew up in Barsana, near Krishna's Nandgaon, and her love for Krishna is celebrated as the highest form of devotion in the Bhagavata tradition and the poetry of Jayadeva, Surdas and the Vaishnava saints.
How it is celebrated
Devotees fast until midday, the hour of her birth, and worship Radha with Krishna. The image is bathed with panchamrita, dressed in new clothes and adorned with flowers, and offered sweets and fruit. In Barsana the Ladli Ji temple on the hill is decorated, the abhisheka is performed at dawn, and the town fills with pilgrims, songs and dance. In Vrindavan the feet of Radha in the Radha Raman and Banke Bihari temples are shown, it is said, only on this day. In ISKCON temples it is Radhashtami.
Many believe that worship of Krishna is incomplete without Radha, and that his grace is reached through hers.
Radha in devotion
In the Gaudiya Vaishnava tradition Radha is Krishna's own power of love (hladini shakti), and the devotee prays to serve the two together. Devotees greet each other with 'Radhe Radhe', and her name is chanted before his.