Go to the course page
Look for the assignment and click on it.
The assignment icon is a hand holding a document.
Your tutor will have named of the assignment (or added some other text) to identify this assignment submission point.
Read the submission statement
Check the box to accept the terms
You can drag your document from your desktop to the submission box
And click the 'Save changes' button
The submission status shows that your document is now uploaded to the assignment.
If you see an 'Edit submission' button, this means that you can make changes to your submission until the cut off date for the assignment.
However, if you see a 'Submit button' you will need to click this before the submission is complete.
After you have clicked the Submit button you will not be able to make changes to your submission.
(The tutor has chosen this method of submission when they set up the assignment)