Navigate to the assignment in the the course view and click on its title.
Read the instructions for the assignment.
Near the "Upload a file" label you will see a small upload form. Click on the "Browse" button.
When you click "browse" a selection of files will appear that are on your computer. Locate the correct file and select it.
Locate the file you wish to upload from the folders on your computer, the click the "Upload this file" button.
Your submission is complete.