Click “Add Notes, URL, or Attachments”.
Do any of the following:
Add notes: Click Add Notes, then enter your note.
Add a URL: Click URL, then enter a web address or other URL.
Attach a file to an event: Click Attachments, then select a file to attach. You can also drag a file to the event info window.
Preview an attached file: Select the file, then press the Space bar.
Remove an attached file: Select the file, then press the Delete key.