I would also recommend Ray Tracing in One Weekend [1] if you want a very quick introduction, and Physically Based Rendering [2] if you want to then go really in depth.
Highly recommend Physically Based Rendering. As a book, Pbrt is to the study of path tracers, as Gravity is to the field of general relativity. Wholly encompassing and rigorous.
[1] https://raytracing.github.io/
[2] https://pbrt.org/