Sri Caitanya Mahaprabhu instructed Lord Nityananda and Haridasa Thakura to spread the Sankirtana Movement-to inspire people to chant Krsna's names and worship Him, and to spread Krsna's teachings.

suno suno nityananda, suno haridasa
sarvatra amar ajna koroho prakasa
prati ghare ghare giya koro ei bhiksa
bolo krsna bhajo krsna koro krsna- siksa
Sri Caitanya-Bhagavata, Madhya-khanda 13.8-9

Listen, listen, Nityananda! Listen, Haridasa! Make My command known everywhere! Go from house to house and beg from all the residents, "Please chant Krsna's name, worship Krsna, and teach others to follow Krsna's instructions."

Along with the Hare-Krsna mahamantra, Mahaprabhu would especially chant the following prayer during sankirtana:

hari haraye namah krsna yadavaya namah
yadavaya madhavaya kesavaya namah

gopala govinda rama sri madhusudana
giridhari gopinatha madana-mohana

hare krsna hare krsna krsna krsna hare hare
hare rama hare rama rama rama hare hare

Nityananda Prabhu performed sankirtana throughout Gauda-mandala with Haridasa Thakura and thus spread krsna-prema through prema-nama-sankirtana. He opened the nama-hatta, community and house kirtana programs, for the welfare of the lost people of the age of Kali.

nadiya-godrume nityananda mahajana
patiyache nama-hatta jivera karana

During these programs, the mahamantra was the primary kirtana sung.

hare krsna hare krsna krsna krsna hare hare
hare rama hare rama rama rama hare hare

sei dvare acandale kirtana sancare
nama-prema-mala ganthi paraila samsare
Caityanya-caritamrta, Adi-lila 4.40

Mahaprabhu spread kirtana even among the untouchables. He wove a wreath of the holy name and prema, with which He garlanded the entire material world.

kali-kalera dharma–krsna-nama-sankirtana
krsna-sakti vina nahe tara pravartana
Caityanya-caritamrta, Antya-lila 7.11

The essential and primary dharma in the Age of Kali is the chanting of Krsna's holy names, especially the Hare-Krsna mahamantra. Unless empowered by Krsna, one cannot propagate the sankirtana movement.

As recorded in Caitanya-Bhagavata (2.23.75-78), Mahaprabhu instructed the devotees:

apane sabare prabhu kore upadese
krsna-nama maha-mantra sunoho harise

hare krsna hare krsna krsna krsna hare hare
hare rama hare rama rama rama hare hare

prabhu kohe kohilam ei maha-mantra
iha japa giya sabe koriya nirbandha

iha hoite sarva-siddhi hoibe sabara
sarva ksan bolo ithe vidhi nahi ara

The Lord ordered everyone in great happiness, "Listen to the krsna-nama-maha-mantra: Hare Krsna Hare Krsna Krsna Krsna Hare Hare Hare Rama Hare Rama Rama Rama Hare Hare. Do japa of this mantra a prescribed number of times. All perfection will be attained through this. Chant this mantra at every moment- there is no other rule:"

Mahaprabhu also instructed Tapana Misra (Caitanya- Bhagavata, Adi-lila 14.143-145):

sadhya-sadhana-tattva je kichu sakala
hari-nama-sankirtane milibe sakala

harer nama harer nama harer namaiva kevalam
kalau nasty eva nasty eva nasty eva gatir anyatha

hare krsna hare krsna krsna krsna hare hare
hare rama hare rama rama rama hare hare

Everything is accomplished by harinama-sankirtana, including the goal of life (sadhya) and the means for its attainment (sadhana). In this age of Kali, the only means for deliverance is the chanting of the names of Hari. There is no other way, there is no other way, there is no other way. Hare Krsna Hare Krsna Krsna Krsna Hare Hare Hare Rama Hare Rama Rama Rama Hare Hare.

Sri Caitanya Mahaprabhu gave the essence of His teachings and instructions to Sri Raghunatha dasa Gosvami in the following verse:

amani-manada hana krsna-nama sada labe
vraje radha-krsna-seva manase koribe

Give honor to all others and don't desire respect from anyone. Always chant Krsna's names, and in your mind, serve Radha-Krsna in Vraja.

Our Gosvamis and Guru-varga pray to always have darsana of Mahaprabhu in sankirtana:

hare krsnety uccaih sphurita-rasano nama-ganana-
krta-granthi-srent-Subhaga-kati-sutrojjvala-karah
visalakso dirghargala-yugala-khelancita- bhuja
sa caitanyau kim me punar api drsor yasyati padam
Sri Caitanyastakam verse 5

When will Sri Caitanya Mahaprabhu, whose tongue is always dancing by loudly calling out 'Hare Krsna!'; who counts the names which He is calling out on the wonderful strip of cloth from around His waist which has been tied with knots for chanting; whose eyes are so large that they seem to reach His ears; and whose arms extend down to His knees-again become visible to me?

Praying for the mercy of Sri Guru and Vaisnavas.