I don't have the experience to answer on shader programing, all I know is it makes everything look better in the long run

But bump mapping is very interesting. If you look at a texture, it's flat, there's no depth to it. What bump mapping does is take a gray-scale bump map and apply it to the texture. You can think of it like a height map, different shades of gray make for different depths of bump, making the texture appear 3d with actual depth, despite it still being a 2d surface.

(I like that phrase fr some reason "different depths of bump" I think I'll use that whenever I bump a thread)