First create a Google Application as following
1- Go to this link: https://code.google.com/apis/console

2- If it is the first time to create a project click on create project

3- Name your project and then click on create project

4. click on the created project link



5- Click create new client ID



6- Turn on Calendar API


7- set redirect url to http://YOURDOMAIN/admin/googlecalendar.php and enter other settings as well




8- Copy both CLIENT ID and CLIENT SECRET


9- paste in socialapisettings "http://YOURDOMAIN/admin/socialapisettings.php" page as follow