As mentioned in the last tutorial, think of layers as pieces of transparent paper. Each layer in a Photoshop image is essentially an entire image itself. By combining these layer images together, you get a composite created of several individual images.
If it’s not open already, fire up the Bing logo file you created in the last tutorial.
Then, open the Layers palette if it’s not open already. You can do this by selecting Window ▶ Layers from the main menu.