I sure understood you. I'm not talking about the command line
within SmartFTP. I'm talking about the DOS-like command line from Windows, the one you can launch from the Start Menu -> Programs -> Accessories -> Command Prompt (or similar, I don't have an english Windows version). In that prompt, change to the SmartFTP directory an run "SmartFTP.exe <FTP site>" to connect to the site upon startup.
As it seems you are not familiar with the command line, it might be easier for you to create a new shortcut to SmartFTP, go to the shortcuts's properties, and specify the FTP site as a parameter to "SmartFTP.exe" there.
Also see:
https://www.smartftp.com/forums/viewtopic.php?t=6348