Rendering refers to processing an XML document to present it with the desired formatting. A style sheet performs transformations and describes how information should be presented. There are three main types of style sheets: CSS, XSLT, and DSSSL. XSLT allows advanced formatting like reordering elements and is more complex than CSS, which only supports basic formatting. XSLT uses elements like value-of, for-each, and sort to select and format data from an XML document according to template rules.