Kirtan comes from the root Kirt, which can be literally translated as recite, narrate, describe, mention, etc. However, in its more colloquial use, Kirtan refers to the practice of call-and-response chanting or singing.
HOW DOES IT WORK?
Strictly speaking, this Practice is at its most effective when you don’t know much about the “meaning” of the words; when your Mind cannot DO anything with the content. Kirtan affords you a reprieve from the incessant internal-monologue of the Mind. If you notice words in your Mind which you understand, then you can rest assured that you have lost focus on the mantra and return to the chant. Kirtan is an opportunity to be free from sense-making, as you drop into a more purely-sensorial experience. In this capacity, it functions in a manner similar to many other well-known forms of meditation.
In a more traditional sense Kirtan is a chance for those who are not shy about embracing their inclination toward the Divine to directly offer praise and gratitude; to reach out for and feel connection with the Transcendent. Kirtan is a mainstay on the path of Bhakti-Yoga, the Yoga of Devotion. Various sects in India and throughout the world may focus that devotional energy on a specific aspect of the Divine, but as a Practice, Kirtan is not limited to any particular denomination or dogmas.
Ultimately, however, more than anything else, Kirtan is a dialogue with Love. Imagine the person (or Beings) you wish you could to talk to more than anyone or anything else in the entire Multiverse, across all dimensions of Space and Time, and treat Kirtan as an opportunity to speak to them; directly. Tell them, through the various Mantra presented, exactly what it is you wish to say. And, perhaps more importantly, allow yourself to Listen for the reply.