Here is a link to a government site with information about 'entry visa'. It will explain how and where to apply for a visa. Many people staying less than 90days may be exempt. It will depend on where you were born, where you now live and what nation's passport you are travelling with?
Entry Visa to India
Here is a useful link that does a quick check to let you know if you need a visa at all. It can be used for all countries
www.visaornot.com
For USA citizens the policy has changed from obtaining a visa directly from the consulate. Check this website
