I know of two things that I thought were good and they are intro level and maybe a bit more advanced but interesting, so I’ll just post the important bit, albeit reworded, of my other comment for visibility in case it helps anyone or whatever.

The first is Why is the Penis Shaped Like That? and other reflections on being human by Jesse Bering. It’s a sort of lighthearted approach to male bodies and other weird quirks of being alive, written by a research psychologist, as well as a columnist for science communication publications like Scientific American. He’s also a gay man who really likes penis stuff. I cannot not mention that, because he himself mentions it as part of his credentials within various articles.

The second is a book mostly about how penis things go wrong, testicular torsion, various kinds of erectile dysfunction and how they get fixed and stuff, it isn’t strictly informational, more like case studies that have been anonymized. It’s called Why Men Fake it, the totally unexpected truth about men and sex by Abraham Morgentaler, a urologist and sexual dysfunction specialist.

Both of these are good not super scientific explorations of things you may want to know, but don’t. I learned a lot and enjoyed the process.