We usually find dīkṣā translated as “initiation” because to “initiate” something is to start it, to set it in motion – and dīkṣā is the thing that starts us in a certain direction.

In bhakti-yoga, dīkṣā is the thing that starts our devotional practices, sādhana-bhakti. Dīkṣā is the beginning of yoga. By dīkṣa we are accepted into a “school” of yoga and begin to be given whatever techniques and materials the school employs in its educational process.

Dīkṣā must be followed by śikṣā, specific and personalized instructions on the school’s philosophy and objectives, and similarly personalized instructions on how to employ the techniques and materials (given through dīkṣā) to realize that philosophy and obtain those objectives.

Dīkṣa and śikṣā are compulsory. In any field, to be guided by an expert is essential, but in bhakti-yoga it is absolutely mandatory because the primary subject (pure love, uttama-bhakti) is so subtle and elusive, and so foreign to our current nature.

There is a single practice which comes before this dīkṣā and śikṣā, it is called śrī-gurupādāśraya – to seek (a) competent guru(s). Of course, some education(śikṣā) is required at this stage as well. Thus śikṣā precedes and proceeds from dīkṣā. The śikṣā prior to dīkṣā however, is less personalized and more focused on basics like learning to identify a guru, and determine the most optimum school for one’s current level of “study.”

There are essential and non-essential components of dīkṣā.

The Essential Components of Diksha

The most essential component of dīkṣā occurs in the heart. The disciple decides to accept someone as his or her GURU, guide, sacred teacher – and that person decides to accept the disciple as his or her ŚIṢYA, pupil, sacred student.

The next most essential component of dīkṣā is that the guru transfers specific techniques and materials to the disciple – that he or she will use as the basis of their spiritual discipline and practice. Usually this is gradual, the guru giving the disciple new techniques when he or she is competent and ready for them. In gauḍīya-bhakti-yoga, the most essential among the materials is Śrīmad-Bhāgavatam and the most essential among the techniques is kṛṣṇa-nāma-saṁkīrtana and specific mantra, especially the two Krishna-mantrabeginning “kṛṣṇāya govindāya…” and “kāmadevāya vidmahe…”

These two components are the essence of dīkṣā. Without them, “dīkṣā” is not dīkṣā.  Other components often accompany dīkṣā – to make it more emotional impactful and significant for the disciple, and to help the disciple in other ways. Here are some of those components:

The Non-Essential Components of Diksha

Disciple and Guru express their commitment to one another vocally and/or symbolically, before witnesses – often including sādhus, sacred fire, and the sacred mūrti. 

Guru gives (a) mark(s) to the disciple that visually identify him or her as a member of the school. These often include the following: a specific  tilok mark on the forehead, a specific name, tulasī necklace (and also for kṛṣṇa-nāma-saṁkīrtan), and a specific tattoo or brand.

All of these components are helpful but none are absolutely essential to dīkṣā.

Vraja Kishor dās

Source...https://vicd108.wordpress.com/2016/01/04/diksha-whats-diksha/