GtkProgessBar Example ??

Hello, I have tested a little bit with the Progressbar. I had no real success. The example in the documentation was not very helpful. It is working but when I try to apply a progressbar to my Program I have no success. I calculate in a loop how far the process is (in %) and want to tell the progressbar the percentage. I don't understand the adjustment and my problem was, that I just see 0% at the beginning of my loop and then just 100% at the end :-(. Is there are refresh function I have to call ??? Or is it easier to just draw a growing rectangle ? Help :-) --Holger