How do i get that silent sound on an acoustic guitar?? example linked?

It's called 'muting'. You either use the palm of your pick-hand and lay it against the strings to mute the sound when you strum, or you use your other fingers to lightly touch the strings but not pressing down too hard because that's what makes the sound when you strum. It's kind of hard to explain but you can youtube tutorials of muting as well.