Lighting can be used to create visually complex and breath taking scenes. One of the massive benefits of having a lighting system is the ability it provides to add extra details to your scene, which wouldn't have been possible otherwise. One way of doing so is using normal maps.
Mathematically speaking, the word normal in the context of a surface is simply a directional vector that is perpendicular to said surface. Consider the following illustration:
In this case, what's normal is facing up because that's the direction perpendicular to the plane. How is this helpful? Well, imagine you have a really complex model with many vertices; it'd be extremely taxing to render said model because of all the geometry that would need to be processed with each frame. A clever trick to work around this, known as normal mapping, is to take the information of all of those vertices and save them on a texture that looks similar to this one:
It probably looks extremely funky, especially if being looked...