In Ray Tracing in One Weekend, you will build a simple brute-force path tracer. Continuing with Ray Tracing: The Next Week, you will add textures, volumes (like fog), rectangles, instances, lights, and support for lots of objects using a bounding volume hierarchy (BVH). Finally, with Ray Tracing: The Rest Of Your Life, we'll dive into the math of creating a very serious ray tracer.

Looks like a great guide on ray tracing.