If you need to pass the commands automatically, you can do that by piping them. For instance, you could do something like this:
echo "cd directory\nget blah.txt\nquit" | ftp
user@ftp.blah.com
This method is dependant on everything going as it should though and I wouldn't recommend it if you can just do it interactively. And don't forget the quit command. The program will just stay open if you don't.