Whats pages do I need to read to find the answer to your question?
There is no page number where you can find the answer to those questions. In order to answer Rev’s (and my) questions and deal with the topic you must understand the subject.
I believe that we can safely say that modernity began with the intellectual movements of the 15th century - but it is a blended change. The Reformation is a good example of modernity versus the post-medieval period, and it expresses itself in many different forms, but basically what we are talking about is a change in cultural worldviews. For example, modernity rejected tradition in favor of rationalization, feudalism in favor of capitalism.
I believe post-modernity took root after WWII. I say this because the struggles of that era called into question many of the ideals associated with modernity (e.g., human perfectibility). Postmodernity, then, is a movement away from modernity. It is more apt, for example, to accept the tradition that modernity rejected, however it will accept those traditions on its own terms.
So I cannot give you a page number, but I can give you sources to read and study. David Wells is one, but another is Brian McLaren’s (for an example of postmodernity) A Generous Orthodoxy and A New Kind of Christianity. Both of those books teach heresy, but they also show you the postmodern mindset in regards to Christianity.
My view is that the Bible carries a worldview of its own, which stands in contrast to these shifts in worldly understanding - and it is a worldview that we don’t alter to make more acceptable to the world. My understanding is that it is supposed to be this way as we are salt and light. It is more important to study these things, IMHO, not for evangelism but to realize the impact our own culture will have on our understanding if we are not aware of those influences. But you need to stop looking through books for answers and instead read and study them so that you can understand the topic.
With postmodernity, you will never find a clear cut definition because it is a departure
from something. It is a moving target as it leads to something else. It would be a mistake to believe that everyone from a younger generation holds a postmodern view, that postmodern views are the same, but there is a trend away from modernity (that's why, perhaps, evangelistic methods don't work...people are ultimately individuals who have unique issues and views of reality).