Hello David
FTP or File Transfer Protocol is a very old protocol, and actually predates TCP/IP networks by about 10 years! The first specification of the protocol was published in 1971 in RFC 114. Over its 50+ year history, the protocol was used extensively in the past to transfer large files over IP networks. As a client-server model, users would log in to the server and issue commands that would send and/or receive files.
Today, FTP is used less often. Indeed HTTP/HTTPS is used to transfer relatively small files over a web interface (depending upon the application in question), but FTP is still often used in website maintenance, backup, and data transfer tasks, especially in environments where its vulnerabilities are not a primary concern. You’ll also find it extensively used in universities, and research organizations as well.
For more info, take a look at this NetworkLessons note on FTP.
I hope this has been helpful!
Laz