In trying to write an answer to this question I kept going off down vast warrens of metaphysical rabbit holes not strictly related to the opening question, so I've tried to begin again and keep it more directly relevant. Tried. 
General Creation Beliefs
Most faiths share a belief in the general idea that humans (and other parts of existence) were shaped from the Song by a god/gods/supreme force, but the details differ. Most peoples do believe in a single (or in some cases dual) creator deity or force as the immediate source of the created world (which is generally conceived of as the Dream), although they may also believe in many other gods and spirits who subsequently came into being and helped shape and take charge of various aspects of the Dream. All of existence is typically thought of as a dream of the Song -- a dream created from the notes of the Song, and enlivened by its resonance.
God(s) and the Song
Beliefs about this creator god or force and its relation to the Song vary quite a bit.
Many believe that the Song and God/s are two separate types of entity, coeval with one another, and that the God/s took the already existing Song and used its/their immense power and will to manifest the Song in a vast variety of material forms. Others believe that the God/s and the Song share the same essence, and that the Song is a direct emanation of God.
Still others believe that what is now the Song existed only as a great discordance of unharmonized notes before the God/s took them and shaped them into the Song. Alternatively some believe instead that there was only darkness and silence at the beginning of all things, and that the God/s created/dreamed the Song itself into being, and then created the Dream from the notes of the Song.
Some peoples believe that, after having given physical form to the most fundamental harmonies of the Song, the God/s or its/their helpers then used these simpler physical forms -- mud, dust, water, etc. -- to shape humankind.
Most of the peoples of the Sirdabi Caliphate believe that The One True God, Dreamer of the Dream, has dreamed humanity directly into being along with the rest of the world. All things in the world are considered distinct manifestations of different parts of the Song, with humanity representing the manifestation of one of the most complex and beautiful portions of the Song, which includes among its many strains the great harmony of Reason which enables mortalkind to understand the world and the will of God and to live virtuous lives (if they so choose).
Azadi & Kalentians
Most Azadi and Kalentians believe that the Song is an emanation of/from the One True God, rather than something entirely separate from it. The One True God then gave material representation to the Song by dreaming a world of material substance through which the Song might manifest, as seen in the Dream's many worldly parts -- its physical objects, energies, and living creatures.
Orthodoxy establishes that humanity and the world are patterned after the Song and resonate with it, but do not partake in the Song directly; i.e., the divine essence of the Song is not an actual part of each human being. They represent parts of the Song, but are not the Song itself. While humans therefore cannot strive for perfect union with God and the Song, they can strive for perfect resonance with it, which is what many mystics and ascetics seek. However, there have been various heresies that have declared that all the world and its creatures, including humankind, do in fact partake directly of the Song and therefore of God, and that as a result all mortals possess strains of divinity within themselves. (Some pagans believe something like this as well.)
Nirzalites
Belief about the creation of the world varies among Nirzalites, as she is worshiped across Idiri by a great many people whose beliefs and modes of worship otherwise differ quite a bit. Most do not believe that Nirzali herself is the creator/dreamer of the world, only that she has taken on a special role as a steward of humankind in the wake of the world's creation by some other god or force. However, a relatively small number of Nirzalites within the caliphate have come to identify Nirzali with the One True God Itself, and so do believe in Nirzali as a creator god/the Dreamer.
Elestaarianism
Elestaarians believe that the God of Good Thought took the vast discordance that existed before the beginning of time and arranged it into the Song, giving order to what had been chaos. The God then dreamed the material world into existence, patterning mortalkind after the most harmonious strains of the newly-arranged Song. But this order is always threatening to lapse back into formlessness and disharmony again, and it is the good deeds and thoughts of Hama Zabadi and Its human helpers that keep the Dream and its underlying Song beautifully shaped and harmonious. God's faithful helpers also work tirelessly to increase the amount of order and harmony in the world until eventually, through the work of God and mortals together, the Dream becomes perfected and remains so for all eternity.
TL;DR
In the end, the average Avarian wouldn't tend to think too hard about the precise nature of the God/s, the Song, and the Dream, and how exactly they relate to one another. They would simply accept that there is a god/gods/creative force, which dreamed the world and its peoples into being according to the harmonies of the Song. Further myths, details, and metaphysical speculations exist, but this is the foundation of belief for most people.
