Intergrating Google API's in a simple Rails app

Hello everybody,

want to create 3 rails apps in which every app has a Google API. 1) Gmail API 2) Google+ API 3) Google calendar API

somebody know how to begin with? Thx!

That depends entirely on where you're starting from.

Do you know Ruby? Do you know Rails? Have you ever written a web application before? Have you ever used APIs?

The place to start with Google APIs is with their documentation.