How does FTP uploads or multi servers work...

So I purchased an image hosting script called ImgShot from a website called CodeCanyon.

Anyway this script features an FTP Upload/multi server feature. Does anyone know how exactly can I set this up?

I tried setting up on some random shared hosting accounts I have but I couldn't get it to work.
Does anyone know how this can be set up and how it works? For example would I be able to run the image hosting script on hostgator shared hosting, but have all the images save onto a server with digitalocean.com or some other hosting provider?

well, from the screenshot i see you need to provide the ftp hostname, user and pass so the script can login to the ftp

then in next fields simply fill the folders properly and it should work

what problem you are facing exactly? any error or something?