The example is a note to Mary from Fred, stored as XML:
<note>
<to>Mary</to>
<from>Fred</from>
<heading>Question</heading>
<body>This sentence contains three errrors can you find themm</body>
</note>
The note has a root element <note> and tags to indicate a header, message body, sender and receiver information.
But this XML document does not DO anything. It is just information wrapped in XML tags.