Boy most of the servers I work with anymore don't allow FTP because it's totally insecure! But delving into the depths of my memory...
The commands available are going to vary, depending on the daemon that's being used on the server. If you want to see what commands are available, just typing a question mark ("?") from the ftp prompt will usually generate a list.
If you aren't sure what a particular command does, you can usually type "help command_name" (replace "command_name" with the actual command you want info on; for example "help mkdir" will give a brief description of what mkdir does).