A userbox is a small box that looks like this, and can come in many styles.
Userboxes are for decorating your userpage and to tell little details about yourself. They have become a fun tradition on Wikipedia. Userboxes help other Wikipedians to know a brief summary about you; you can tell other Wikipedians that you come from Switzerland, that you like classical music, etc.
There are hundreds of premade userboxes to choose from.
And it is easy to design new userboxes. They require just three things to make them: the userbox template, the name of an icon image page, and a blurb that you type in. To see the code for the userbox included here click "Edit" on the toolbar above.
It is possible to create links to every word in an article. But providing too many defeats their purpose by obscuring the most relevant links. Here's an example of overlinking:
The above passage hides the relevant link. Compare that with this:
Wikipedia's greatness stems from being able to link articles together easily, but don't overdo it. It can get really annoying and does not help the reader.