The "Feeling Good Handbook" is a companion book to the author's earlier book "Feeling Good" which taught its readers how to identify distortions in their thinking as a way to recover from depression.
I read both of the books at the same time. There is a lot of overlap between the two books, and you could certainly read one or the other by itself, but I found that I got more out of them by reading them together.
The first book ("Feeling Good") goes into the theory in more detail. The second book ("Feeling Good Handbook") applies it to more situations -- not only to depression, as in the first book, but also to various kinds of anxiety, including such common fears as public speaking and test taking.
The Handbook also takes more of a workbook format, with spaces for you to write stuff down, something that the author constantly nags you to do. This can be humorous at times, and annoying at other times, but I found it did work (usually) in getting me to actually stop and do the exercises.
The techniques I learned have been very useful for me, especially in dealing more patiently with everyday annoyances and in learning not to be so reflexively hard on myself.
There is also a big section on anti-depressant medications in the back of the book (the author is neither totally for nor totally against the use of medications -- he lets his patients decide) -- this section is actually in both books -- but I suspect that it is partially out-of-date by now. I didn't use that section anyway, and it's really just a tangent to the main part of the book.