I don't know how to upload a document. Do I just copy and paste or is there a button on the screen?
You don't mention if you are an instructor wanting to upload the file for your students, or a student trying to upload a file as an assignment submission. I'll try to answer both situations.
As a teacher you can easily upload and add files anywhere you have the Rich Content Editor, such as on a Page, Announcement, Assignment, Discussion, etc. Here is a quick guide about how to do that How do I insert course files into the Rich Content Editor using the Content Selector as an instructor?
Files can also be added directly to Modules if you'd like How do I add assignment types, pages, and files as module items?
As a student, if you are trying to submit a file as part of an Assignment here is a guide How do I submit an online assignment?
Or if you are trying to attach a file to a Discussion; there should be a button or link below the entry box for the discussion if it's been enabled by your instructor. By default though it's not possible to attach documents to discussions.
I hope one of those suggestions answers your question.
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