I understood how to write Running OAuth 2.0 code for the client side.
Using existing Authorization Server, like Google, seems to be not too complicated.
Question
The best reference is the OAuth 2.0 site. They list the available server libraries that you can use. Currently, the options are:
Java
PHP
Python
Other
I would also highly recommend that you read all the documentation available on how the standard works before getting started. There are many parts to OAuth and it can get confusing. At least, that's how I feel.