For non-fiction, Machinery of freedom focuses on the legal system and how private security firms operate and settle disputes with private arbitrators.
The type of anarcho-capitalism you're probably familiar with is the Rothbardian moral perspective.
His idea of anarcho-capitalism is one where legal philosophers determine the optimal laws to be put into place and then the courts must abide by them.
David Friedman on the other hand presents a legal system in which law is generated on the market by private security firms(what police were SUPPOSED to do) and private dispute arbitrators(what courts were SUPPOSED to do) rather than by a state monopoly on both, So that whatever laws form in certain towns and cities is based on their local customs.
If you don't feel like reading the whole book and simply want a quick summary, give this a watch:
https://www.youtube.com/watch?v=jTYkdEU_B4oA good fiction book to read is The Moon Is A Harsh Mistress, by Robert A Heinline. It's the book that actually inspired David Friedman's concept of Polycentric Law.