Make sure your project you just created is selected in the Projects menu just right of ‘Google APIs.’ Then click on the main menu.
Select IAM & admin > Service accounts:
Enter an account name and optional description. The account ID will be automatically generated.
After you create the service account you’ll need to create a key.
Make sure you check on the radio button for your json private key. You can leave the Role unspecified.
Click Create and the json will download. Store it in a secure place, as you will need it later in the setup.
Next Step: Enable the APIs