An exported list is usually received via email within a few minutes. If not received, first check your spam folder. If not there, your email filter may have quarantined the incoming email. The export may have also been sent to a different email address than what you were expecting. You can verify which email the export is being sent to by clicking your portrait on the bottom left > User Settings.

If the email is correct, but the email is not being received, you can change the email address in User Settings and process the import again. The email address can be changed back afterward.

This can happen is Safari is your default browser. Safari will just show the raw data of the file. To save as a CSV file (spreadsheet), click File > Save As...

Name the file in the Export As: field

Format: Choose Page Source