To access your web via FTP, please download some of the FTP programs such as Cyberduck or Filezilla.
When you login, the port is 21 and the username/password is the same as your cpanel.
If you are creating an addon and would like to know on what is the
username/password for the FTP, please go to your Cpanel -> FTP
Accounts and click on Configure FTP Client for each account