To add an environment background
The background is not yet visible in the Scene View.
The background is now visible. This is because this type of background is made up of two parts, the Sky image and the background Environment shader that points at the image; the two elements link together automatically.

Once this is complete, moving around the model will see the background moving appropriately in real-time. With a modern graphics card, if there are reflective surfaces in the scene, setting the Presenter Hardware Shading in the Options Editor to Lighting will show the newly set up background reflected in all such surfaces (see Presenter Page).