Step 1: Login/Register your Google account
First, you have already signed in to your Google account.
Then go to this link: Google Cloud Platform
If you first go to Google Cloud Platform, Google will ask you to agree to their Terms of Service. Select a country
I agree... 
Accept and continue.
Then create a new project by clicking Select a project (or the name of the current project - also in that position).
Click New project.
Fill in the basic information for your project, then click Create.
Next, go to OAuth consent screen
External
Create
Fill in the following fields and then click Save and continue
Application home page: the link to your homepage
Application privacy policy link: the link to the Privacy Policy page of your website
Application terms of service link: the link to the Terms of Service page of your website
Developer contact information
Step 3: Set up a credential for your project
Go to Credentials
Create credentials
OAuth client ID
Choose an application type of Web application.
Fill in the Name field. (You should use your website's name)
Go to Authorized JavaScript origins and fill in theadd URL field like below:
Change your-website to your website domain, then click Create.
You will receive the Client ID and the Client Secret for your website.
Follow this guide to finish set up Login with Google.