Geometrical optics (at the level we are doing it) is relatively simple plug and chug for the most part. Know the law of reflection, refraction, thin lenses, plane mirrors, cameras, magnifier, microscopes, and the eye. Things can be much more technically difficult than what we are seeing here … but this is sufficient to give you the idea of how things work and provide you with enough background to dig deeper if needed. Watch signs in thin lens problems. Make sure you understand the basic diagrams of the instruments.