This is a great question and I completely agree with you. Too often people give very difficult definitions of postmodernism. In light of this, let me offer you a few points that will help you understand postmodernism.
First, postmodernism does not believe in a totalizing grand narrative. In other words, postmodernism resists the idea that there is a dominant perspective. M. Foucault, one of the great voices of postmodernism, speaks of the archaeology of knowledge. By this he means that there are many different perspectives that are valid.
Second, in light of this, there is a hermeneutic of suspicion. This means that there is a suspicion when it comes to anything that claims to be objective. Postmodernism realizes that all people are coming from a point of view, based on their experiences and historical context. Here is a great quote by Michel Foucault:
"Each society has its régime of truth, its ‘general politics’ of truth: that is, the types of discourses which it accepts and makes function as truth; the mechanisms and instances which enable one to distinguish true and false statements, the means by which each is sanctioned; the techniques and procedures accorded value in the acquisition of truth; the status of those who are charged with saying what counts as true."
Third, there is an emphasis that all knowledge is relative. These three points should get you started.