There is no real-time instant method yet for crypto to fiat currencies and vice-versa. You have to establish a chain like first make account on exhcange coinbase or bittrex, then you have to go through process of KYC, eventually after that you would be able to buy from your deposit method.
If you want multiple deposit methods, you can try kraken also, as a 2nd preference
RE: Whats the fastest way to buy Ethereum in India????