This site is dedicated to web FTP protocol manuals, guides and ebooks.
What is FTP itself? You may get the explanation here: en.wikipedia.org/wiki/File_Transfer_Protocol.
All the needed information you may get at the following resources: tldp.org, filetransferplanet.com or ftpguide.com.
It may be useful if you are new to ftp.
If you have the beginning skillsets you may try other useful resources as "Guide to FTP" at oacs.umd.edu.