Google ID is a unique identifier associated with your Google account. It is required e.g. to unlock Factory Reset Protection in FAMOC.
Admin has to enter propper Google ID in a Security options section in a Policy. Once it is done devices associated with this policy can be unlocked with account provided.
To obtain your Google ID go to this link. Make sure resourceName field value is people/me. Click Execute.
Log in with your Google account and authorize Google APIs Provider when asked.
The 21-digit number shown in the bottom left box is the ID of the account you logged in with. This number should be entered in the policy template.