What is a TGC File Type?
To create a TGC file, right-click on an aspect of the scene (objects, water, atmosphere, etc.), select Save nodes as clip file... name your TGC file, choose your save location, and click Save.
To insert a file, select File → Insert Clip File..., navigate to your TGC file, and click Open. You can also click on different aspects of the scene (cameras, lighting, objects, etc.) on the right, select Insert file Clip..., navigate to' to your TGC file, and click Open.