Using XML data with XSLT

[Susannah]

I am a novice, so this is probably a very simple question. I have used the API to generate an XML file of titles by a certain author, and I have created an XSLT stylesheet to display the data. When I learned XML and XSLT, it was always in the context of MODS or Dublin Core, so I am used to having to declare a namespace for the XML schema. Do I need to do that with the Goodreads XML dataa? I can't get any of the harvested data to display, but my code validates. I would really appreciate any feedback.