If your instructor allows file uploads as a submission type, you can upload a file from your computer as an assignment submission. 

Any attachments added as part of a graded assignment submission are also copied to your user files but are not counted against your user quota. However, once the file has been uploaded as a submission, you cannot delete the file. Files are stored in the Submissions folder.

If your institution has enabled Google Docs as a submission type, you can also upload a file from Google Drive.