PsychEducation | Treating the Mood Spectrum is very helpful for explaiing bipolar., especially BPII. He has written a book that I think is out of print but everything in the book is on the webpage. (The webpage probably has more now).

When I was diagnosed 14 years ago it was this site that helped me understand what I was going through, taught me about meds and how they were affecting me and helped me learn how to cope as I adjusted (I'm BPI so it wasn't a perfect fit but it was still extremely helpful).