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.
My collection of scripts to create skies, stars and planets. I’d done a few images like this which seem popular, so I thought for myself and for others, I’d put together a series of scripts to generate these things randomly. This creates a good starting point for your creations, they can be used as backgrounds for images in JWildfire, or other graphics programs where you need a sky or a starfield etc