I am an event supervisor and at the bottom of the test creation environment I see that I can import different types of files.  Is there a guide on how I can use this import feature to import a previously written test?

You cannot import tests. They do not have the same formats. You can copy/paste each question from your previous tests. Make sure to paste as 'Clear text'. Right-click in the editor, select 'Paste as clear text'. You can upload supporting documents but not tests.