The File Transfer Protocol (FTP) protocol is a set of rules followed by a client and a server for the purpose of transferring files. The standards specification of the FTP protocol is defined in RFC 959.
An FTP server is an implementation of the server side of the FTP protocol. You can upload files to an FTP server, and you can download files from an FTP server. There are several users that can belong to the same FTP server. Some FTP servers are anonymous, and some require authentication.
The FTP protocol runs over one command port, and one data port. The command port, as its name implies, is for commanding what to do. For example move to this directory, give me a list of files/directories in that directory. Download this file. Upload that file.
The data port is for transferring files. FTP provides both a passive mode and an active mode. If you are using active FTP. Then your local computer will host the server for the data connection. If you are using passive FTP, then the server of the command side will also host the server of the data connection.
SFTP is FTP over SSH. It has nothing to do with the standard FTP protocol; however, it does provide much of the same functionality. You can transfer files to and from the SFTP server.
FTPS is yet another variation of FTP and it stands for File Transfer Protocol over SSL. This is the exact same protocol as FTP, but it is over SSL (SSL is a layer on top of TCP which provides encryption). There are 2 types of FTPS. Implicit and Explicit. In implicit FTPS, all communication starts by using SSL. In explicit FTPS, a command is made to the FTPS server using normal FTP over TCP to start using SSL. In FTPS you can also have CCC and CDC mode. This stands for Clear Command Channel (command channel is not encrypted) and Clear Data Dhannel (data channel is not encrypted).
If you have a server, you can buy an FTP/FTPS/SFTP server to host on your server. If you have hosting for your web page somewhere, they will typically allow you to use FTP to upload your files to that web server.
Several websites may have upload/download of files available, but it is not considered to be FTP/SFTP/FTPS.
Brian R. Bondy