Postmodernism Art favors being more free that past Art, instead of figures and objects sitting for portraits or oil based landscapes, Postmodernism created a new way of thinking and making art, artists were allowed to be a lot freer and the basic rules of Art were thrown into the rubbish bin, Jackson Pollock is an example of an Artist who instead of working in a standard basic way, use the rules of Postmodernism to create their work in a positive way.
While postmodernism seems very much like modernism in these ways, it differs from modernism in its attitude toward a lot of these trends. Many modernist works try to achieve something by trying to change the world in some way, meaning is important in Modernism, most artists using the Modernism approach find they are trying to create meaning out of the world in a productive manor. Postmodernism, in contrast, doesn't think about the world in anyway, but rather celebrates that. The world is meaningless? Let's not pretend that art can make meaning then, let's just play with nonsense and enjoy it.