How do I get a list of everyone who opened an email and export that list to an excel sheet?
An Opened Email filter in a smart list would show you everyone who ever opened an email if you us the "is any" selection in the drop down where it asks for the email name. You could then use the export button (see screenshot) to export the list. Depending on the size of your database though, this may be an extremely large list, and may not export successfully. You would then need to use constraints on your filter to cut down the number of leads, possibly by the date they opened the email, or by picking specific emails.