FTP(File Transfer Protocol): FTP is one kind of protocol. It is a standard Internet protocol for transmitting files between one computer to another computer among the Internet. You can use Windows, Linux but I will discuss windows PC. If you can get a file instant from a specific  address and even if you can store. If you think you have one workstation. There are lots of computers there and several users. But they want to store files in one specific Server PC and they will get data file from a server PC then need to FTP server.
On the other hand, you have lots of software, movies, and song if you want to access through the internet cloud then need to FTP server. If you want to access from different internet clouds and different networks then need to real IP.
How to FTP server setup with windows 7,8:
How to FTP server setup with Filezilla software:
