Please use the space below to tell us about your skills and experience and how they satisfy each of the criteria in the person specification.
-> So far, so good, sounds like a standard cover letter
You might find it helpful to use the person specification criteria as headings to structure this section.
-> Does this mean I should provide a document with bullets and subheadings in place of the cover letter?
As Scotia says, most places want to see *exactly* how you fulfill the essential and desirable criteria -- this one is just nudging you a bit further towards the bullet points and subheadings.
However, check whether the online form will allow you to do bullet points and subheadings. Plenty of HTML form submission routines either barf over non-text formatting, completely ignore anything that isn't a hard carriage return or use an idiosyncratic set of their own commands for formatting (why yes, forum software, I am looking at you).
It'll also be useful for you to write out structured document that shows how you meet all of the criteria, then give that and your full CV to somebody with experience in applications -- as it's not always the most recent stuff that often goes in a covering letter that best fulfills the criteria on the person spec. You can still structure the document as a narrative rather than as bullet points, but it should be a thematic narrative that addresses the essential criteria in the order given in the person specification.
For teaching or research posts, applicants should also upload a separate document or CV into the "Document Upload" section, setting out teaching and research interests and publications (including the title, reference and date of each publication).
-> This part confuses me. Would they like a CV, a document or both? If I were to supplement my CV with such a document, would it not be with the information that I already intend to include in a cover letter?
Does your CV contain a statement of research and teaching interests? If it doesn't, you should probably add those sections to the CV before uploading the CV. I recently dug out an extremely ancient academic CV of mine (I seem to recall that it was the one that got me a lectureship in 1994 ;-) in a rootle through my computer's filesystems, and my research and teaching interests covered about 3/4s of a page in 11pt palatino.