A framework can be used to help speed up development. It does this because all the generic coding (DB, Authentication etc) has already been done, so you don't have to use up valuable time recoding unnecessarily and also you don't really need to fully test each bit as you know it should work, saving time (time=money these days).
However, most frameworks implement some fairly advanced programming concepts like MVC, Active record etc, so using these frameworks as a new php'er (or even a veteran coder) can seem daunting at first if you dont understand them.
Its true that most frameworks have manuals but until you have come to grips with the basic ideas of these advanced concepts it will most likely leave you baffled.
Anyway for Zend, there are a few video tutorials that you may find useful.
Zend Framework
I belive there are similar for CodeIgniter too, but I haven't checked
I personally don't really use frameworks, I usually find they are too big and cumbersome for what I need and I find it quicker just to fudge something together from my own code base rather than studying a vast and complex framework to get simple things done.