Hello @CarolFaul and welcome to the Instructure Community! My guess is that your professor has uploaded a file in a format like PowerPoint, which you can open using Keynote on a Mac. Another option you have is to upload the file to Google Drive, which can open files in a variety of formats.
But most important, please contact your professor! You might not be the only student who's encountered challenges with the lecture, and by letting them know you will help everyone in the class.
I’m going to mark this reply as a solution. I realize it does not solve your problem, but it will help our colleagues who have a similar question.
