Can you really break a glass with your voice and if so, how?

Yes, but with difficulty. The science behind it is that all objects have frequencies at which they naturally vibrate - you know that annoying rattle in your car that tends to be worst at certain speeds? These frequencies are called resonant frequencies. When a singer makes a note sound waves travel through the air as a pressure wave which we hear because it makes our ear-drum vibrate in sympathy. In the same way a wine glass will vibrate. If you can hit the resonant frequency of the wine glass, by singing just the right note, and make the note loud enough, eventually the glass will try to vibrate more that the material is able to and it will shatter.