Harinama-sankirtana (the congregational chanting of the holy names of the Lord) may be most familiar from seeing the devotees out in the streets, dancing and chanting the maha-mantra Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare accompanied by mridangas (two headed drums) and karatalas (hand cymbals). Krishnas holy names are endowed with all of His potencies and this sound vibration can reawaken a person to his spiritual identity and existence. We have forgotten our real identity as spiritual beings, part and parcel of Krishna, and this forgetfulness is the root cause of all our suffering. When a person is asleep he forgets who he really is and in his dreaming he assumes one illusory identity after another, in each existence suffering unnecessarily.
500 years ago Lord Krishna came as Sri Caitanya Mahaprabhu (or Lord Gauranga). He appeared as a devotee of Krishna (Himself) to reawaken all the conditioned souls by the method of harinama-sankirtana. He would go with His followers into the streets and chant the names of Krishna so that peoples suffering could be ended, and they could take to the real activity, the spiritual activity, of worshiping and serving the Supreme Lord.