:Put your finger to your throat, and then say the word "thing."  Notice you don't feel any vibration during the "th".  That is a "voiceless" consonant.  Now, with your finger still on your throat, say the word "this."  Your throat will vibrate during the "th" sound.  That vibration is coming from your vocal cords, and the absence or the presence of that vibration determines whether the consonant sound you make is "voiceless" or "voiced" respectively.