Between the time you submit the final manuscript and the time that it’s published, some months may pass. My publisher, for example, needs half a year to organize and produce the book. But why does is take so long, you might ask, and what role do you play in the process?
The final manuscript might go through further editing or evaluation (possibly multiple times). Then at some point, the typesetting needs to be done. Here you come into play again: you will receive the proofs, which you will need to correct. Look out for wrong typesetting or layout, typos and other things that need to be changed. However, don’t edit the text again in a more thorough way. If you do, the typesetter has to work more than necessary. The publisher will likely charge you an extra fee if you make to many changes (e.g. editing entire paragraphs or chapters, changing the structure). In order to correct the proofs, the publisher will probably give you specific instructions for how to do it.
Afterwards, the publisher will create all the more formal things such as the front matter at the beginning of the book, including the copyright page, the cover, and so on. If not yet defined, you might be contacted in order to discuss the book’s title and subtitle (the book title used so far has been the ‘working title’). The publisher will start to fill in databases with the sales information and prepares marketing material such as flyers and websites. Whatever else needs to be done, there’s will be a lot going on behind the scenes that you might not be aware of. Finally, the book is usually printed by a printing company somewhere else and subsequently distributed. And that takes time, because your book is not the only one being produced at that time. But you know the publication date, so relax and think about and work on your next projects.