Here is guide that describes how to submit a Goodle Doc for an assignment. The steps for submitting a Dropbox file are similar, just select theDropBoxrepository instead ofGoogleDocs, andLogin to your account.
Click the title of the assignment on the main course page.
Click theAdd submission link below the assignment description.
After clicking the add button, theFile pickerwindow appears.
From theFile pickerwindow, click theGoogleDocsorDropBoxlink on the side menu.
There is aLogin to your accountbutton that you click to login and select the file. After logging in, click a file name to select it.
After selecting it, it should appear in the window as the submission.