Click the red Edit Meeting button and then click Attach File button. It will be green if there are no files already attached, and red if there are.
Once the file uploading area is open, you can click the "Upload New File" drop-down and choose the right category, then click the Browse button to go find your file. Again, make sure it's properly named so it will sort in the table of files on the other page. Save Changes.
If you want to remove a file from this event (but not delete it from the site) you can check the checkbox next to any file that's already attached.
Appears in: Calendar Module , Files Module