When a book’s chapters are written by different authors, you should cite the specific chapter you are referring to.
When all the chapters are written by the same author (or group of authors), you should usually cite the entire book, but some styles include exceptions to this.
In APA Style, single-author books should always be cited as a whole, even if you only quote or paraphrase from one chapter.
In MLA Style, if a single-author book is a collection of stand-alone works (e.g. short stories), you should cite the individual work.
In Chicago Style, you may choose to cite a single chapter of a single-author book if you feel it is more appropriate than citing the whole book.