Additional FTP accounts are most commonly used to give others access to an account for the purpose of sharing a web development project. You can setup additional FTP accounts very simply using the Control Panel. Simply log into your Control Panel and select 'Additional FTP Accounts' from under the 'Files' section. 

To add a new FTP account simply specify the username and directory name (within your public_html directory). If you don't enter a directory name they will have access to your whole account. 

To edit or delete an existing account you can use the 'Modify An FTP Account' utility on the same page. 

NOTE - On some account types this feature may not be available.