The service account is an account, like a user account. The difference is the service account belong to a project (you have the project ID in the @....). The user account is a Google account, managed by Google or by your administration.
Then, except where the account is attached, there is no other difference: you can grant roles and permissions on it. As a user account. When you have created it, if you grant no role, the service account has no permission, even on its host project.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…