OpenGL provides us with not one, but three different types of lights we can make, directional lights, point lights and spot lights. I will try to teach you about how each is different, and how to use them.
Now you have your scene looking a little nicer with some lighting, but all objects are a gray colour. Here we will learn how to assign materials to shapes to change how they look under different lighting conditions.
Flatly colouring shapes is perfect, if we want an unrealistic look to our scene. But for realism, we really want to add some sort of lighting system. You can learn here how to use OpenGL's lighting system for a more realistic scene.