A) If Online text is ticked, students can write something in a text box to be included with submission.
B) If File submissions is ticked, students are able to upload a file with their submission, this enables options D and E.
C) If Submission comments is ticked, they can leave a comment along with their submission, this may be so that they could request feedback, or to give instruction in the case of a complex submission.
D) Decide how many files a student is allowed to submit.
E) Decide what the maximum file size is that students can submit, please note submissions over 20mb, can not be marked by turnitin.