The FTP area deals with all the tools relating to setting up and managing FTP accounts, as well as managing FTP sessions. FTP (File Transfer Protocol) is a method by which you can transfer files between computers, usually using the Internet. There is a huge amount of information stored on FTP servers around the world that can only be accessed by using FTP. When using FTP you use an application called a "client" to connect to a machine called a "server".
CPanel allows you to set up FTP accounts so that certain external users can access a restricted part of your system. You can also set up an anonymous FTP account so that anyone can access a restricted part of your system. You can also manage these FTP sessions, cutting them off if they go on for too long.
Warning: FTP, by its very nature, allows external users to modify your web site (albeit a restricted area of your web site). External users can upload, download, and delete files. Keep this in mind when you set up an FTP account.