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".
There are a large number of FTP software packages available. Some of them are built in to your browser (such as Internet Explorer), others are dedicated applications (such as such as CuteFTP or WS_FTP), while still others are built into web applications (File Manager in CPanel is one example). Generally speaking, if you are going to spend a lot of time using FTP or have a large amount of files to upload/download, a dedicated FTP client is the way to go.
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.