How do we setup Organization in GCP?

The answer to your question is YES (partially). When we use Gmail account an organization resource will be created automatically for us. To understand this better, please read below excerpts from google docs:

https://cloud.google.com/resource-manager/docs/cloud-platform-resource-hierarchy#organizations

1) If you are new to Google Cloud and have not created a project yet, the organization resource will be created for you when you log in to the Google Cloud console and accept the terms and conditions.

2) If you are an existing Google Cloud user, the organization resource will be created for you when you create a new project or billing account. Any projects you created previously will be listed under "No organization", and this is normal. The organization resource will appear and the new project you created will be linked to it automatically.

https://cloud.google.com/resource-manager/docs/creating-managing-organization#acquiring

Hope this was helpful!