Google Cloud Platform (GCP) uses a specific resource hierarchy. At the very top, you have an organisation, tied to a domain (for example: mrtrustor.net). Inside that organisation, you can have folders and subfolders. Finally, you have projects, which can be inside folders, or directly under the organisation node. Projects are where your cloud resources (VMs, databases, etc.) actually live. By default, projects are completely isolated from one another, especially at a network level.
Classic network topology Typically, in a classical infrastructure, network architects design multiple networks according to the security wanted for the elements residing in the network. For instance, for a web infrastructure, you could have a front network, where the webservers live, which is accessible from the Internet on ports 80 and 443 ; and a back network, for the database servers, which is only accessible from the front network. This is a fine design, because it allows you to manage security between the networks with firewalls and routing restrictions.