FTP stands for File Transfer Protocol, and is one of the standard methods by which files can be moved from a local computer to the internet to be publicly-viewable. Many programs are available that can utilize FTP to move files around, many of which are free or low-cost options.
For the Microsoft Windows platform, Internet Explorer (installed on every system running Windows) can be used as an FTP client in addition to fetching internet pages as normal (HTTP client). See this article for more information on configuring IE for FTP use.
Other options for Microsoft Windows that can be installed on your local computer to connect to an FTP site include:
By default on a Macintosh computer you can use the Terminal application and connect using the Unix FTP command-line utility (if running any version of OS X), though this does not have a graphical interface, and is likely daunting unless you are a programmer who uses Terminal frequently already.
Other options for Macintosh computers include: