Hāsya, adbhuta, vīra, karuṇa, raudra, bhaya and bībhatsa—the seven indirect mellows—are explained in the Bhakti-rasāmṛta-sindhu (4.1.6). The hāsya-bhakti-rasa, laughing devotion, is explained as follows:
vakṣyamāṇair vibhāvādyaiḥ puṣṭiṁ hāsa-ratir gatā
hāsya-bhakti-raso nāma budhair eṣa nigadyate
"When through devotional service a laughing attachment to Kṛṣṇa is developed, it is called hāsya-bhakti-rasa by learned scholars."

Similarly, adbhuta-rasa is described in the Bhakti-rasāmṛta-sindhu (4.2.1):

ātmocitair vibhāvādyaiḥ svādyatvaṁ bhakta-cetasi
sā vismaya-ratir nītādbhuta-bhakti-raso bhavet
“When one's general attachment is fixed in wonder, it is called adbhuta-bhakti-rasa.”

Vīra-bhakti-rasa is described as follows (B.r.s. 4.3.1):

saivotsāha-ratiḥ sthāyī vibhāvādyair nijocitaḥ
ānīyamānā svādyatvaṁ vīra-bhakti-raso bhavet
yuddha-dāna-dayā-dharmaiś caturdhā-vīra ucyate
"When attachment to Kṛṣṇa mixes with the bellicose tendency, the charitable tendency or the merciful tendency in the heart of the devotee, such devotion is called vīra-bhakti-rasa."

(Sri Caitanya Caritamrta-----2:19:187-----purport).

Foolish people try to concoct knowledge by manufacturing something in their brains. That is not the real way of knowledge. Knowledge is śabda-pramāṇa, evidence from the Vedic literature. Śrīla Vyāsadeva is called Mahāmuni. He is also known as Vedavyāsa because he has compiled so many śāstras. He has divided the Vedas into four divisions—Sāma, Ṛg, Yajur and Atharva. He has expanded the Vedas into eighteen Purāṇas and has summarized Vedic knowledge in the Vedānta-sūtra. He also compiled the Mahābhārata, which is accepted as the fifth Veda. The Bhagavad-gītā is contained within the Mahābhārata. Therefore the Bhagavad-gītā is also Vedic literature (smṛti). Some of the Vedic literatures are called śrutis, and some are called smṛtis. Śrīla Rūpa Gosvāmī recommends in the Bhakti-rasāmṛta-sindhu (1.2.101):
śruti-smṛti-purāṇādi-pañcarātra-vidhiṁ vinā
aikāntikī harer bhaktir utpātāyaiva kalpate
(Brs. 1.2.101)
Unless one refers to śāstra (śruti, smṛti, purāṇa and so on), one's spiritual activity simply disturbs society. There is no king or government to check people, and therefore society has fallen into a chaotic condition as far as spiritual understanding is concerned. Taking advantage of this chaotic condition, many rascals have appeared and proclaimed themselves incarnations of God. As a result, the entire population is indulging in sinful activities such as illicit sex, intoxication, gambling and meat-eating. Out of many sinful people, many so-called incarnations of God are emerging. This is a very regrettable situation, especially in India.

(Sri Caitanya Caritamrta-----2:20:353-----purport).

This verse is found in the Bhakti-rasāmṛta-sindhu (1.2.2). Because living entities are minute, atomic parts and parcels of the Lord, devotional service is already present within them in a dormant condition. Devotional service begins with śravaṇaṁ kīrtanam (S.B.7:5:23), hearing and chanting. When a man is sleeping, he can be awakened by sound vibration; therefore every conditioned soul should be given the chance to hear the Hare Kṛṣṇa mantra chanted by a pure Vaiṣṇava. One who hears the Hare Kṛṣṇa mantra thus vibrated is awakened to spiritual consciousness, or Kṛṣṇa consciousness. In this way one's mind gradually becomes purified, as stated by Śrī Caitanya Mahāprabhu (ceto-darpaṇa-mārjanam (CC.3:20:12). When the mind is purified, the senses are also purified. Instead of using the senses for sense gratification, the awakened devotee employs the senses in the transcendental loving service of the Lord. This is the process by which dormant love for Kṛṣṇa is awakened.

(Sri Caitanya Caritamrta-----2:22:105-----purport).

One should not partially study a book just to pose oneself as a great scholar by being able to refer to scriptures. In our Kṛṣṇa consciousness movement we have therefore limited our study of the Vedic literatures to the Bhagavad-gītā, Śrīmad-Bhāgavatam, Caitanya-caritāmṛta and Bhakti-rasāmṛta-sindhu. These four works are sufficient for preaching purposes. They are adequate for the understanding of the philosophy and the spreading of missionary activities all over the world. If one studies a particular book, he must do so thoroughly. That is the principle. By thoroughly studying a limited number of books, one can understand the philosophy.

(Sri Caitanya Caritamrta-----2:22:118-----purport).

Thus the total number becomes thirty-nine. To these thirty-nine should be added five others: association with devotees, chanting the Hare Kṛṣṇa mahā-mantra, reading Śrīmad-Bhāgavatam regularly, residing in Mathurā, the birthplace of Kṛṣṇa, and worshiping the Deity with great respect and veneration. The thirty-nine items plus these five come to a total of forty-four. If we add the previous twenty items to these forty-four, the total number becomes sixty-four. The five items mentioned above repeat previously mentioned items. In the Bhakti-rasāmṛta-sindhu, Śrīla Rūpa Gosvāmī states:
aṅgānāṁ pañcakasyāsya pūrva-vilikhitasya ca
nikhila-śraiṣṭhya-bodhāya punar apy atra śaṁsanam
"The glorification of these five items (association with devotees, chanting the holy name and so on) is to make known the complete superiority of these five practices of devotional service."

The sixty-four items of devotional service include all the activities of the body, mind and senses. Thus the sixty-four items engage one in devotional service in all respects.

(Sri Caitanya Caritamrta-----2:22:129-----purport).

Above that, there is association with devotees, and after that there is initiation by a bona fide spiritual master. After initiation, when one follows the regulative principles of devotional service, one becomes freed from all unwanted things. In this way one becomes firmly fixed and gradually develops a taste for devotional service. The more the taste grows, the more one desires to render service to the Lord. In this way one becomes attached to a particular mellow in the Lord's service—śānta, dāsya, sakhya, vātsalya or madhura. As a result of such attachment, bhāva develops. Bhāva-bhakti is the platform of purified goodness. By such purified goodness, one's heart melts in devotional service. Bhāva-bhakti is the first seed of love of Godhead. This emotional stage is there before one attains pure love. When that emotional stage intensifies, it is called prema-bhakti, or transcendental love of Godhead. This gradual process is also described in the following two verses, which are found in the Bhakti-rasāmṛta-sindhu (1.4.15–16).

(Sri Caitanya Caritamrta-----2:23:13-----purport).

In the Bhakti-rasāmṛta-sindhu (1.3.41, 44), rati (attraction) is thus described:
vyaktaṁ masṛṇitevāntar lakṣyate rati-lakṣaṇam
mumukṣu-prabhṛtīnāṁ ced bhaved eṣā ratir na hi
kintu bāla-camatkāra-kārī tac-cihna-vīkṣayā
abhijñena subodho ‘yaṁ raty-ābhāsaḥ prakīrtitaḥ
"The real symptoms of the fructification of the seed of love (rati) are manifested because the heart is melted. When such symptoms are found among speculators and fruitive actors, they cannot be accepted as real symptoms of attachment.... Foolish people without knowledge of devotional service praise such symptoms of attachment even when they are based on something other than a desire to serve Krsna. However, one who is expert in devotional service calls such symptoms raty-ābhāsa, a mere glimpse of attachment."

(Sri Caitanya Caritamrta-----2:23:45-----purport).

In the Bhakti-rasāmṛta-sindhu (2.5.1), sthāyi-bhāva, permanent ecstasy, is thus described:
aviruddhān viruddhāṁś ca bhāvān yo vaśatāṁ nayan
su-rājeva virājeta sa sthāyī bhāva ucyate
sthāyī bhāvo ‘tra sa proktaḥ śrī-kṛṣṇa-viṣayā ratiḥ
"These moods (bhāvas) bring under control the favorable ecstasies (such as laughing) and unfavorable ecstasies (such as anger). When these moods continue to remain as kings, they are called sthāyi-bhāva, or permanent ecstasies. Continuous ecstatic love for Kṛṣṇa is called permanent ecstasy."

(Sri Caitanya Caritamrta-----2:23:46-----purport).

In the Bhakti-rasāmṛta-sindhu (2.1.4–5), the following definition is given:
athāsyāḥ keśava-rater lakṣitāyā nigadyate
sāmagrī-paripoṣeṇa paramā rasa-rūpatā
vibhāvair anubhāvaiś ca sāttvikair vyabhicāribhiḥ
svādyatvaṁ hṛdi bhaktānām ānītā śravaṇādibhiḥ
eṣā kṛṣṇa-ratiḥ sthāyī bhāvo bhakti-raso bhavet
"Love for Kṛṣṇa, Keśava, as previously described, reaches the supreme state of being composed of mellows when its ingredients are fulfilled. By means of vibhāva, anubhāva, sāttvika and vyabhicārī, hearing and chanting are activated, and the devotee is able to taste love for Kṛṣṇa. Then attachment for Kṛṣṇa, or permanent ecstasy (sthāyi-bhāva), becomes the mellow of devotional service (bhakti-rasa)."

(Sri Caitanya Caritamrta-----2:23:47-----purport).

In the Bhakti-rasāmṛta-sindhu (2.1.14), vibhāva is described as follows:
tatra jñeyā vibhāvās tu raty-āsvādana-hetavaḥ
te dvidhālambanā eke tathaivoddīpanāḥ pare
"The cause bringing about the tasting of love for Kṛṣṇa is called vibhāva. Vibhāva is divided into two categories—ālambana (support) and uddīpana (awakening)."

In the Agni Purāṇa it is stated:

vibhāvyate hi raty-ādir yatra yena vibhāvyate
vibhāvo nāma sa dvedhālambanoddīpanātmakaḥ
"That which causes love for Kṛṣṇa to appear is called vibhāva. That has two divisions—ālambana (in which love appears) and uddīpana (by which love appears)."

(Sri Caitanya Caritamrta-----2:23:51-----purport).