Step 1: Go to google api credentials. Take your OAuth cilient id and secret key, its here You can use wizard on quickstart page.
Step 2: Enter your client id and secret key to application/config/calendar.php file
Step 3: Set your application base_url on application/config/config.php
Ready! its run.
You must enter authorization redirect URI in your google api project settings. For example http://yourhost/auth/oauth login progress in auth/oauth url