A neat "book" i came across courtesy of @itsfoss.
"Putting the 'YOU' in CPU" explains how a CPU works, how computers run programs, and the basics of these wonderful devices that have taken over our life, in simple (ish) terms.
For anyone that wants to know HOW computers do what they do, this is a great place to start, and it's free, readable on the website, on GitHub, or as a downloaded PDF.