Ray tracing is relatively easy to understand, it's not ray tracing that is actually complicated. Ray tracing is simply sending out rays from the virtual camera, seeing what they hit along the way, and calculating the lighting effects of the materials and light sources when you hit those things. In the end you've simulated a sample of light that hit the camera. Repeat a couple million times and you've got an accurate picture of what the virtual scene looks like.

"Normal" computer graphics is comprised of doing every dirty shortcut trick you can imagine to avoid tracing hundreds of millions of rays per second while still having some semblance of lighting effects in the virtual scene.