Deogenesis

While The Primeval Gods were born in the Void, and the Old Gods from the undifferentiated energies of The Firmament, the Young Gods were, and are, born where divine energy is shaped by will.
Deogenesis begins with an accumulation of divine energy called a Divine Egg. Once formed, an egg can wait for centuries, accumulating additional power, until it comes into contact with sufficient intention to catalyse its awakening. Once awakened, the new god must secure sources of additional power of it wants to grow.
There are two ways to gain done power. One is to find and-consume other divine eggs, or lesser Gods. The former is somewhat frowned upon in what might be called divine circles, and the latter is quite beyond the pale, as it is one of the only ways that a god can actually die. The other way for a god to grow is to form bonds with mortals through the codification of sacred acts. By performing these acts in worship of their god, a congregation filters a small part of the boundless power inherent in The Primeval Gods' creation and transmits it to the subject of their worship.
On rare occasions, a divine egg coincides with a living creature, usually bonding with them before birth. Such an individual begins to manifest increasing power through their childhood, until the power matures. At this point they have a choice, either to accept the power, or to pass it, willingly, to another.
A being of sufficient power can consume a divine egg, living or otherwise, and will either be utterly destroyed by the process or become a god.

Deoplasticity

Young Gods, whatever they might claim, are not a fundamental part of the universe. Instead, they find their place in one of two ways.
Creator Gods pour a large part of their power into creating a lineage. Whatever happens in the future, the creator remains a part of their lineage and draws power from their success, as well as from their worship. Only one lineage is known to have deliberately broken this bond, when the Orcs rose up and kileld the thirteen Dark Lords.
Culture Gods have a much more reciprocal relationship with their follower. On the one hand, they teach their followers words, rituals and even skills which become sacred, thus influencing their chosen people. On the other, in order to secure their influence, they have to present themselves in an appealing way, and adapt that presentation as the culture develops.
This quality of adaptation - referred to by scholars as deoplasticity - can be manipulated by the god's followers. Through a mixture of fervour and repetition, worshippers can sanctify their own words and rituals, forging a new bond and even forcing the god to alter its nature to benefit from that bond.
Over time, a god can develop aspects, different versions of itself which commune with different groups of worshipper. There is a cost involved in maintaining aspects, but if a god decides to abandon an aspect, it can be adopted by another deity who will then benefit from the assocuated sacred acts. A god who spreads their influence too thin finds themself unable to grant powers; a god who abandons too many aspects becomes isolated, and risks losing all of their followers to others.
It is also possible for more than one god to share a single aspect, as often happens when a cult wants to enforce a single focus on a diverse congregation. Humans, who have never known their creator, seems to be especially adept at exploiting deoplasticity.