The echo mode is how characters you type are echoed to the screen. You select one from from the 3 available modes: one star, three stars and no echo.
The default mode is one star.
KDE su can remember passwords for you. You can enable this by checking the "Keep password" box. If password keeping is enabled, you only need to enter root's password once for each command. You also have to enter a timeout value; this is the amount of time a password is kept.
The default not to keep passwords.