Prophase is the 'P' in "PMAT." The 'P' also stands for "Prepare." The centrioles in the nucleus start to move to the opposite edges of the nuceus that they are currently in. They are preparing to go to their new nucleus. A way that you can remember the way that the chromosomes work is by using this scenario. You can think of it as a couple who got divorced (that part will come in later on in the Anaphase step) and they are planning on moving out of their home because niether of them can pay the bill without the other. Then they move out and they find a new home (which happens in the Telophase step of Mitosis.) This scenario will make more sense later on when you know about all of the other steps in Mitosis. The spindle fibers (remember SPIDERS) start to reach toward the nucleus and more importantly the chromosomes. The necleus' envelope starts to break down because the nucleus will disappear so that the cell can create 2 more nuclei.
This picture shows what the step Prophase looks like.