SFTP is where you can add, delete, and edit website files directly. For instance, you may use SFTP to delete a plugin that has disabled your site completely. 

Developers may request SFTP access to your website. Only give this information to individuals and companies that you trust. Irreversible damage can be done through SFTP. 

Software Access Option: FileZilla
Mode: SFTP (not regular FTP)
Host: sftp.flywheelsites.com
Port: 22
Access: request an SFTP login from Smart Inbound