You can only upload files to a test if your teacher has chosen this option in the test settings. Your teacher will let you know if you are required to upload any files to your test.
It's possible to upload files:
If your teacher wants you to upload notes per test, you will see the upload option on the main test screen.
If your teacher requested you to upload notes per question, then you will see the upload option once you open one of the test questions:
Choose a file, for example, a picture of your handwritten notes, and upload it by clicking on the "Start" button.
You will know that the file is uploaded when there is a little preview picture on the left, and the red Delete button on the right side:
To remove the picture and upload a different one, click on Delete and then follow the upload instructions to choose a different file instead.