Best way to access my asp.net Data from multiple mobile app

I'm new to mobile development! I have a web application with several users. I want to build multi-platform mobile app. I consider using phoneGap to build the app.

My question is how can I make the user login and retrieve all his data to mobile app? I know people talking about OAUTH (htt开发者_运维百科p://oauth.net/code/) to do the user verification.

But How can I get all the user data? Please someone guide me, I really appreciated.