FTP is defined as a protocol that allows users to copy files between their local system and any system they can reach on the network.
In simpler terms, you can use ftp to upload files from your comp, and make it accessible for the world wide web. Let's say you have a subdomain, like
http://juiceisgood.retroness.comIf they enable you to use ftp, you can use your ftp address to log in, then you can upload files and whatever file you may have will turn out like this:
http://juiceisgood.retroness.com/mydumbpic.jpgx]
Hope that helps.