Hello Mujib,
First of all, sorry for my delay on the answer and thanks for your interest on the project.
There are a couple of resources that I can recommend you to start with Turpial. The first one is the official documentation of libturpial [1]. libturpial is the library that does all the heavy work behind the client and understand all the protocols and APIs of external services. That would be the starting point if you want to implement support for any new protocol as facebook.
The other resource is the wiki [2], there you can find instructions to install the development version as well as general information about coding standards, tests, etc.
I hope this information let you start with Turpial, be certain that you can always ask here or in the #turpial channel in freenode about any question or doubt about the code or the development process. Also, you can find me on twitter to as @satanas82.
Best regards