In the Jewish tradition, at the end of the wedding ceremony, the groom stomps on a glass to symbolize the ending of their previous lives together and the start of a new life together, clearing away the shards of the past and opening up to all the blessings of the future.  It means that their bond of love be as difficult to break as it would be to put together the pieces of the broken glass.

When the glass is broken, the guests to all shout “Mazel Tov” which means congratulations and good luck in their very loudest and happiest voices.