Once you have defined a set of parameters (or opened an existing one), you can start the process using the menue Sync->Sync.. or the S-Button on the button bar:
The sync dialog lets you enter the password of the remote server and has the option to perform a dry run. A dry run does everything except executing the ftp commands and is useful to update the status if you already have a synchronized FTP directory (or if you have sent a few files to the FTP server not using WebSync).