Event Notes are text notes that you can add to your events. Each note has full word processing editing features (like font color, size, lists, links, etc.) and when you add them to your event they're shown as a blue "Notes" link. You and your visitors can then click on the "Notes" link to see your notes pop up in a new dialog. See the image below:

Since your events don't have all of the word processing features that your event notes do, you have the option to show your event notes. When you turn this feature on, anything that is in your event notes will be added to the event text and show in your calendar. Follow the steps in the link below: