If you’re a Photoshop guru, you’ll recall back in Photoshop 6 when there was an actual Airbrush tool. That changed in Photoshop 7, when it became an airbrush option in the Options Bar when you have a brush selected. You can always click on the option in the Options Bar to select it, but that’s kind of a pain. The easier way to use the shortcut Shift+Option+P (Mac) Shift+Alt+P (Windows).