An assignment is essentially an activity where the instructor tells the student, "Go do this, and then submit proof that you've done it". Optional features enable the instructor to supply the student with a file, to upload a file, and to submit both feedback and comments. Blackboard will create a link in the assignment, for the student to upload material to the instructor.
Every assignment must have instructions and a student submission. The instructions are entered by the instructor when (s)he creates the assignment. The student submission can be material that the student types directly into the assignment-feedback form, or something that the student uploads (such as a word document or picture).
The instructor can give a student feedback on the student's submission. In return, the student can give the instructor feedback on the assignment. Instructors can also allow multiple submissions, so the student has multiple tries to get it right. No matter how many trials the student...