Hello. Thank you for the question. It sounds like you either have a hot corner enabled to show the desktop, or accidentally pressed the F11 key on your keyboard. To get back to your presentation, try moving your mouse cursor to each corner of your screen (ie - as far to the bottom right corner as you can point your cursor, and do this for each corner). If this does not toggle the desktop, press F11 on your keyboard. Depending on the model Mac you are using, you may need to hold the Function (Fn) key while pressing F11 on your keyboard.