General Information: http://www.psplinks.com/content/General-Information.html

Layers: http://www.srsteele.com/Layers/layers.htm

PSP X Primer, PSPP XI,  Selections, Layers, Masks, Channels, Text, Portraits, Photographs, Composites, Restoration, Art, Keyboard shortcuts, Books, Internet links.

Near the top of each page there are a number of links that will allow you to return to a previous page or to pursue a topic further. In the body of several pages you will find lists of links that will allow you to choose  topics for further study. Most of the imbedded images are represented by thumbnails to speed loading. Click on a thumbnail to see a larger version. To return to the page you were viewing, use your browser's back function.

To learn about layers I advise you to connect to the link, then save all the 280 pages to your my documents folder. Then you can print out sections so that you're not online for a long time.