The Submissions tool allows you to set up folders where students can turn in assignments online. TurnItIn's plagiarism detection service is integrated with D2L's Submissions tool, so you can get originality reports for student's files within the Submission folder. You can also set up your Submission folder so that you can grade files within it and have your feedback automatically transfer to D2L's Grades area.
Can I create a Submission folder for group projects?
Yes. First you have to set up the student groups in your course (see the Groups page), then when you create the Submission folder, select the Group Submission folder setting (see the Creating Submission Folders page). With a group submission folder, all students in the group will be able to see the feedback you enter for the assignment, and the score you enter in the Submisisons grading interface will be transferred to the Grades area for all of the students in the group.
What happened to Dropbox?
In August 2017, D2L changed the title of the "Dropbox" area to "Submissions". This was in an effort to encapsulate what the tool is actually used for. It also reduces confusion with the unrelated website Dropbox.com.