What different language is used to show that you are describing a document vs. supporting your argument with one?
I would definitely recommend looking at the College Board’s official rubric linked here.
The major difference is that describing a document means that you merely summarize a document. But DO NOT QUOTE, as it could result in you not getting the point!
Supporting your argument can mean two things. It could be “Evidence”, where you write a sentence(or two) that connect the document to the thesis. It could also be “Analysis and Reasoning”, also known as HIPP-ing, where you go deeper, writing multiple sentences about the Historical Context, Intended Audience, Purpose of Author, or Point of View, and how it relates to and supports the thesis.