Before connecting to mason.gmu.edu, you will need to set the Default protocol under Connection to SFTP (SSH File Transfer): CyberDuck > Preferences > General > Connection
Open the CyberDuck client.
Select Open Connection in the upper, left-hand corner.
mason.gmu.edu for the Server name. (Note: port should be set to 22.)
Enter your username and password.
Once you have created your folder(s) under
public_html, you can drag and drop folders between CyberDuck and Finder.
For CyberDuck support, see CyberDuck Help.