I am developing an iGoogle Gadget. I have to access the spreadsheet data of logged in user. How do I implement an OAuth for it?
OAuth is just an API that Google gives out to developers to let them authenticate Google accounts in other manners other than just going on google.com - for example through a programmatic way.
Authentication is the basis of it, but through OAuth you're able to retrieve lots of information from a specific Google account (calendar info, contacts etc.)
To implement this you would need to read more on their website: https://developers.google.com/identity/protocols/OAuth2