Typically, you will have to know the ftp site name and the user name and password assigned to you for that ftp site. You will start the ftp session by typing something like:
ftp www.mysite.net
At the ftp prompt, enter your user name and password, if the server requests that you sign in anonymously place "anonymous" or "ftp" in the username field and leave the password field blank. Then use the ftp commands (e.g 'ls' 'put' 'get' 'cd' 'chmod') to transfer and maintain files at your site.
If you prefer a GUI interface, there may be some X Windows ftp clients available for download. Google 'ftp Linux' and see what you can find. I prefer the plain command line version. Much quicker and easier once you learn the commands.