I visit the Corel PSP user forums to read about the problems that others are having and the solutions. A while back there was much discussion on the use of the Histogram and Curves. One of the members (Ronald V.) came up with a tutorial for us to use.The tutorial can be placed in the 'My PSP Files' or the 'My PSP-8 Files' in your 'My Documents' folder and it will show up in the PSP-8/9 program under 'Help' "Quick Quides'. For users of PSP-X, I have not been able to find a way to add it too the program so you can read the tutorial in your web browser. Download the zip file and unzip to the location of your choice.
Download the file