In the Content tab, click on the module you'd like to add a document to and then click on "Create New" at the top right of the page.

Next, click on "HTML Document"

Create your document with text, uploaded files, video, etc. Set a due date, availability dates, and release conditions if you'd like.

Find your document at the bottom of the module content. To edit your document (or others) first click on it, then click on the ellipsis at the top right of the page and click "Edit"