By glancing through the "Table of Contents," you can find all of your assignments. They are designated by a special icon as seen below.
Alternatively, you can access your assignments by clicking on the "Assessments" tab at the top of the course and then selecting "Assignments."

By clicking on the "Assessments" tab and selecting "Assignments" you can see exactly what assignments have been submitted. If an assignment appears as not submitted, you may not have selected the "Submit Assignment" button.

To upload files, you can either use "Drag and Drop," or "File Upload." To review how to use these, follow the link to the "Private files" page.

Remember to select "Save changes" when you are done adding the file.