Go to the Google Developers Console.
Select a project, or create a new one by clicking Create Project:
In the left sidebar, select the APIs item below “APIs & auth”. A list of Google web services appears.
Find the Google+ API service and set its status to ON—notice that this action moves the service to the top of the list.
In the sidebar under “APIs & auth”, select Credentials and in that screen choose the OAuth consent screen tab
In the sidebar under “APIs & auth”, select Credentials.
Click Add Credentials button and choose OAuth 20 Client ID.
In the resulting Client ID for web application section, copy the Client ID and Client secret to your