I'm building a shed in my garden. What I need is to put bikes, a lawnmower, a few tins of paint, a toolbox and some random junk under cover. That's the primary aim of the project. The seconday aim is that it mustn't look too shabby. And finally it mustn't be a lot of work to put up.
Now I know that the raw materials for building a shed are wood and nails, and maybe some glue. But it would be great if some of the pieces of wood came stuck together already, so that I didn't have to do so much hard work to achieve my goals.
Enter the pre-fabricated shed, and ta-da! It takes less than half the time.
Take 'lightboxes' for example. They are a popup window in the middle of your web page to show an image. They can be part of a gallery and include 'previous' and 'next buttons'.
The way a lot of jQuery works is by modifying attributes of existing HTML. Say you have some HTML which looks like this:
<a title="Some random picture" href="pic.jpg">