Bump effect lets you easily simulate surface relief: embossing, leather, stone and so on. You load a height–map and Boxshot simulates the surface according to the loaded image brightness. See the Bump section of the Materials panel.
You can adjust the following parameters:
Normal bump just changes the normal direction, affecting reflection and refraction. It works on reflective materials only, as otherwise there is no way to see how it works. Good for leather, glass, wood effects. Here are three spheres with 0%, 50% and 100% stone bump effect:
This one works on flat surfaces only and takes care about lighting and shadows, so it is great for embossing effects:
While looking great, the effect doesn’t change the shape itself, so it is still flat and it is better to look on it from top.
Note that offset bump is not supported by the hardware accelerated preview. Use the raytracing preview instead to see the effect while editing scenes.