You can create additional FTP accounts in cPanel in the FTP Accounts section under the Files category.

When creating a new account you can specify a directory, this will be the top level directory that user will be able to access.  For example if you set the directory to be:

/home/username/public_html/test

or 

/home/username/test

The user would not be able to access the public_html folder and would be restricted to the test folder only.

When making the FTP account you choose the FTP username which is   something@yourdomain.com and specify a password.

When connecting use that FTP user and password, and the FTP server host name can be the domain name eg yourdomain.com or the server ip address.