There is a lot of free information about using layers in Adobe Photoshop and Elements. Do a search through Google.com for 'photoshop basic layers tutorials' to find great links. Here are some that we found.
Learn the beginning stages of working with layers and tools in Adobe Photoshop/Elements. Jay Arrich refers to earlier versions of Photoshop, but his info is still valid for CS or CS2.
Webmonkey.com is a respected website that posts free tutorials about graphic programs and subjects. They have interesting articles and a glossary reference for Photoshop.
One of the best Photoshop resource sites out there. This site has great tips and news about working in Photoshop. Search the keyword 'layers' to find interesting advice.
There are many training options for Adobe Photoshop, but we like two companies in particular. We can also recommend some great authors and books.
Total Training has been providing DVD-based training to artists for over 10 years. They have training geared specifically to Photoshop or Photoshop Elements. They also have DVD's that cover digital photography.
Lynda.com has been around almost as long and has both online and CD-based training. They also have Photoshop or Elements specific material, as well as a series of 'HOT!' books that are great tie-ins.
Katrin Eismann is a well known Photoshop artist with a series of books. Her 'Photoshop Masking & Compositing' book is a terrific resource about masking (and she loves Primatte for her chromakey work!).
Rhed Pixel is a training and design company run by Richard Harrington. You've seen him lecture at many shows and conferences. Now you can bring him to your home office!