Hi Peter, as Dave said, it's your cPanel login information.
Also: If you login to a cPanel account, you can always go to FTP Accounts (under Files), then under Special FTP Accounts, click the Configure FTP Client link on the right. There you can find your manual FTP settings as well as pre-configured config files for Filezilla and Core FTP for Windows, and Cyberduck for Mac.
Of course if you get stuck, or have trouble accessing your FTP, you can always open a ticket to Support. They're super helpful!