This list (3) shows all the questions that have been created for the specific course. Those with the "Added" tag (4) are the questions added to the specific test you are editing.
If you want to edit a question simply click on it, make the changes you want and then update it.
Clicking on the option "Show questions from other courses" (5), reveals all the questions that you have created in the other courses that you have access to as an instructor.
Note: When you click the delete button (6) the question is deleted from the course (and the system) and not only from the test you are editing. If you want to remove a question from the test, just click on the "Added" button and the question will be removed.