Hey, Vijitha.
Vijitha Kumara wrote:How easy is it for someone new to this to start working with these APIs (Facebook Connect, Google Friend Connect, and the Twitter API).
All of these APIs are built to be easy to implement for beginners. As an example
Facebook Connect is as simple as three steps. The complexity is understanding how to combine these simple interfaces into a rich application using a combination of client-side and server-side scripting. If you have a basic understanding of HTML, JavaScript and a scripting language such as PHP you'll be well away!
Other than books, I would recommend looking at the official web pages of each:
Facebook ConnectGoogle Friend ConnectTwitter API
There are also a number of videos on YouTube and Vimeo of how to implement features such as commenting into web sites.