The simplest thing you can do with XUL is display static text and images. Such content is very easy to add. The <description> tag has powerful line-wrap features but usually only supplies small amounts of text at a time. Images and styles in XUL are very much like HTML. Fancy borders are a Mozilla feature of both, and Mozilla has numerous style extensions, some of which are content- or layout-specific.
XUL without GUI widgets is hardly more than HTML. In the next chapter, you'll see how to add that most famous of widgets, the button. Improving the overall appearance of XUL is also a theme for Chapter 4, First Widgets and Themes.