Here’s a great introductory article on FTP that I found on the AssistProgramming website. The article walks through an example of uploading your website to a server for publishing (ie: transferring the files for your website from your computer to the server).
The article walks through some details of using a file transfer client and has some nifty example screenshots.
Although AssistProgramming uses the SmartFTP client in its example, it also mentions WS_FTP. I have used SmartFTP in the past and it’s pretty good but I believe that the WS_FTP Professional secure file transfer client is easier to use, it’s faster and it’s much much more secure.