It is true that sound can break glass, but it is not as easy as it may look in the movies.

The way sound travels is that it makes things vibrate, so either air molecules or water or whatever the sound is traveling through. If you've ever seen anyone run their finger around the edge of a wine glass you may have heard it sing a note. This sound comes from the 'resonant frequency' of the glass --the vibrations of the particles making up the glass.

All glasses are a little different and so have slightly different resonance frequencies. It is this frequency that will break the glass.

So in order to break the glass you will need something that will produce the same frequency of sound as the resonant frequency of the glass. This sound must be produced loud enough and long enough for all the glass molecules to vibrate enough to actually shatter the glass. I wouldn't recommend trying this at home since the sound may actually need to be so loud that it may cause some damage to your hearing if proper precautions are not taken.