Com How to create your own Weblogs portal with Manila. The text inside the braces is a little script that gets evaluated each time the page is displayed. You already use macros, look in your site template. You'll see lots of little bits of text inside curly braces. Those are macros.
Any web page can have macros.
Here's an example. They are documented here. Where you see dynamic content, it's done with just a macro call. In a sense, with macros, any page can be a template. If you don't like our layout or colors or sizes, you can have it your own way.