First of all, FTP is an abbreviation and means File Transfer Protocol. Protocols are definitions on how exactly communication between endpoints needs to be done. FTP was developed specifically for the transfer of files in a network and was already used for this purpose in 1974. However, the actual "FTP" standard was not defined until 1985 in RFC 959.
With the help of FTP, entire folder structures can be created, edited and deleted on so-called FTP servers. Files can first be uploaded and then downloaded. To be able to use FTP, the command line of the desired operating system is sufficient. However, there are also numerous user-friendly alternatives in the form of graphical FTP clients such as WinSCP or FileZilla.
Thanks to FTP, files can be made available to other participants in a network in a simple and inexpensive way.