Think of tags as like a book index where you find words and which pages they are on, the same principle applies here. Although it's taken a stage further so it might not be the word, but the subject, so for example if you're looking for things to do with fractal gradients for example. A tag may bring back posts with gradient files, as well as posts that discuss gradients, or tutorials about them.
In this tutorial, Brad walks us through the new Z-buffer facility on JWildfire 7.20. This allows the creation of depth maps, which, when loaded with the original image will create wonderful 3D images on Facebook, and some others.