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 Eco Web Hosting Control Panel.
Simply log into your hosting control panel and go to Files > FTP Accounts

From the subsequent page, you can create your FTP user, set the username you want, the domain and the sub-directory you want the user to have access to, you can leave this a public_html if you want the user to access all of the site/files.

Once created you will be able to unlock FTP for the additional user from this page.