Newbie issue: What is a document, and how to extract keywords from them

Hello, I have a workflow (wf.png) that crawls URLs and outputs a single column table of page content in XML (filtered-table.png).

1. How do I convert the XML cells of the above table to documents? 
2. How do use the Keygraph keyword extractor?
3. What other basic things might I be missing?
4. There are many tutorials and example workflows - any in particular ones that reflect my issue?

Thank you