Photoshop 10: Using Layers
The use of layers in Photoshop can be very powerful. Layers are often compared to transparent sheets of paper stacked on top of each other. They allow you to manipulate different parts of an image independently and achieve some very sophisticated results. You can also make certain layers invisible in your *.psd file and save a *.jpg or *.gif image that shows only the visisble layers.
TIP!!! When you save an image with layers, Photoshop saves it an a *.psd format (photoshop document). It is good to save a copy of your image with the layers, because you may want to go back and add or remove certain layers of information at another time. Unless you save it as a *psd file, you won't have the separate layers. When you are done editing you can then select the "Save for the Web" option or other image formats you need.
Take a look at the following image:
Explanation of image example:
For each layer a thumbnail (a very small version of an image) is given to the left. Notice that the Opacity for the red rectangle layer is set to 56%. This is what allows the red border to be translucent and allow the painting below to peek through. You can change the opacity of any layer by changing that value when the particular layer is active.
Note: The following information is associated with an older version of Photoshop, but you might find it useful.