GLB is a file format for 3D scenes and models. It is the binary version of the glTF 2.0 file format.
In the Teachers Dashboard, when you click on the icon to show the 3D model, you will be shown a GLB viewer with the option to download the raw GLB file.
Microsoft Windows 10 has a program installed by default, called 3D Viewer, which can display and manipulate GLB files. This program also allows you to enable Mixed Reality mode, where your 3D models can immersed in the real world.