The Material Viewport displays the Material being edited applied to a mesh. You can interact with the Viewport in the following manner.
Rotate the mesh by dragging with the Left Mouse Button.
Pan by dragging with the Middle Mouse Button, and zoom by dragging with the Right Mouse Button.
Rotate the light direction by holding down the L key and dragging with the Left Mouse Button.
The preview mesh can be changed by using the associated button controls (the shape buttons, Select Preview Mesh combo, and Use Selected StaticMesh button).
The preview mesh is saved with the Material so that the next time the Material is opened in a Material Editor, it will be previewed on the same mesh.
The Viewport of the Material Instance Editor also displays statistics about the Material, such as instruction counts for the various shader types as well as the number of Texture
samples being used by the Material.
If your Material has some kind of movement in it you and you want to preview it, you can enable Real - Time preview by first clicking on the small white triangle to enable Viewport Options and then click on the stop watch icon.
You can also enable / disable real time preview by pressing CTRL + R at the same time on the keyboard.