The Indian visa process varies from country to country. Therefore it is always best to check with the Indian Embassy in your home country as to the specific requirements. It will also vary depending on which type of visa you wish to apply for.
For those travelling on a tourist visa there is an option of ‘visa-on-arrival’ for a number of countries. To see if your country is eligible or not for the e-tourist visa you can go to the following website: https://indianvisaonline.gov.in/visa/tvoa.html

If your country is not included then you will need to apply to the Indian Embassy prior to travel.  Be aware that in both cases your passport must be valid for 6 months from the date of entry.

For more detailed information please refer to: https://indianvisaonline.gov.in/

Duration of stay– Regardless of the duration of the valid visa, the maximum duration of stay in India is limited to 6 months (180 days) on each visit
Extension of stay is not permitted on tourist visa and it cannot be converted into any other type of visa.