XSLT allows you to transform one XML document type to another. For instance, you may have a XML document containing your hours logs for different projects:
XML Hours Log
<HoursLog>
<Entry>
<ProjectName>My XML Project</ProjectName>
<Date>10/3/2003</Date>
<StartTime>10:00pm</StartTime>
<StopTime>4:00am</StopTime>
<Duration>6</Duration>
<Comments>Made new XSLT sheet for translating XML into HTML.</Comments>
</Entry>
<Entry>
<ProjectName>My XML Project</ProjectName>
<Date>15/3/2003</Date>
<StartTime>8:00pm</StartTime>
<StopTime>12:00am</StopTime>
<Duration>4</Duration>
<Comments>Made new XSLT sheet for translating XML into a SVG Image.</Comments>
</Entry>
</HoursLog>
Using an XSLT processor and a XSLT stylesheet, you can transform this dataset into a html document or even an image bar chart. The XSLT processor works as follows: it takes as input a XML document to transform, the XSLT stylesheet defining the transformation, and produces a new XML document.
Detailed Example
A detailed "Hello World" style example may be downloaded to get you started with this useful technology. The download contains everything you need to get started, including the Xalan XSLT Processor for Java (Yes, you can use Xalan from inside your Java programs, cool!).
Download the example: XSLT_Tutorial.zip