Ugadi is celebrated as the first day of the year by people of Andhra Pradesh and Karnataka. On this day new Samvatsara, which is cycle of sixty years, starts. All sixty Samvatsara are identified by unique name.
Ugadi is celebrated as Gudi Padwa by the people of Maharashtra. Both Ugadi and Gudi Padwa are celebrated on the same day.
Ugadi is New Year according to Luni-Solar calendar. Luni-Solar calendars consider the position of the Moon and the position of the Sun to divide the year into months and days. The counter-part of Luni-Solar calendar is Solar calendar which considers only position of the Sun to divide the year into months and days. Because of that Hindu New Year is celebrated twice in the year with different names and at two different times of the year. The Hindu New Year based on Solar calendar is known as Puthandu in Tamil Nadu, Bihu in Assam, Vaishakhi in Punjab, Pana Sankranti in Orissa and Naba Barsha in West Bengal.
The day begins with ritual oil-bath followed by prayers. Oil bath and eating Neem leaves are must rituals suggested by scriptures. North Indians don't celebrate Ugadi but start nine days Chaitra Navratri Puja on the same day and also eat Neem with Mishri on the very first day of Navratri.