FileZilla works but sftp doesn't, how so?

My webhost allows me to create FTP accounts, and I successfully used them with FileZilla to store backup files from my computer on those remote FTP accounts. Now I am trying to upgrade from the FileZilla way of doing things to the more easily automatizable line-command way. So, I do something like this in my terminal : sftp -P 21 myftpusername@myurl.net (I know the port is 21 because my webhost told me so). But to my surprise, the terminal gets stuck with this command and outputs nothing (as of now it has been stuck for 10 minutes, so I'm not holding my breath for it to eventually work out). Usually, I experience the opposite : the pure terminal way of doing things is more efficient than the nice-UI way, because the nice-UI is nothing but a wrapper around the command-line. Any help appreciated.