A few weeks ago I mentioned Photoshop actions when talking about the new Adobe Exchange service, but now I thought many people may not know what they are, how they're installed, how to use them or what kind of results you can obtain with them.
Photoshop actions are code bits you run from within the program itself, containing a series of tasks you can apply as many times as you want on different images. They're usually presented as one file (ATN extension) or batch of files and include menu commands, tool actions, filters and effects you can apply on any photo automatically by simply pressing the "Play" button.
Installing actions is easy: save the ATN file anywhere on your computer (tough I personally prefer to keep all of them in C:\Program Files\Adobe\Photoshop CS\Presets\Photoshop Actions) and then launch Photoshop. Open the image you want to work with and on the History window, click on the Actions tab. You'll see a list of actions that come preinstalled with Photoshop. Now click on the little arrow button on the top right corner and select "Load action". Look for the ATN file you just saved, load it and then press "Play": the magic will begin. Sit back and enjoy while Photoshop automatically works with your images in front of your eyes. Once the action is done, simply save the photo and you're done.
Now that you know how to install and use actions, go ahead and practice a bit! Here's a superb collection of Photoshop actions you can use to create all kind of effects with your photos.