Once you have finished your assignment, you can submit to your instructor for a grade by toggling the purple Submit Assignment button found in the top right corner.
Students are also able to remove their own submissions. The Remove Submission button can be found on the top bar, the same place where you would have found the Submit Assignment button before.
Keep in mind that once you remove a submission, you must resubmit before the final deadline in order to avoid having your work marked as Missed. This way you'll ensure you receive a grade.