The growth of individuals from children to adults incorporates a number of types of mental growth, from the physical maturation of the brain to the construction of frameworks appropriate to create a powerful weltanschauung.The acquisition of a value system is part of this maturation - in present times this normally occurs first by one's parents/guardians ingraining behaviour into their children and then years later a token exploration of values guided by religious or political concerns. A slow but continual exposure to new situations and values follows throughout the rest of most people's life. Inculturation is the process by which values pass from other people to oneself during a period of rapid personal growth as one becomes vested in a society.
Values do not exclusively come from or achieve their particular weights through inculturation - they may also come about through reflective equilibrium (or other types of reflection), through slower social processes of a socially vested person, or through debates. There are also values that have a more biological origin - we may classify the urges, desires, and various things particular to us as a species to be values, and must consider them when constructing our value systems. These biological values have some different characteristics than their more-acquired cousins - among other things they're closer to being default values for our species, although as Freud notes they can (and in many instances should) be tamed or overridden to make civilisation possible. Another partly orthoganal way to divide values lies between those that are primarily self-focused from those that are primarily other-focused - self-focused values are primarily concerned with what one wants for beings in one's identity, while other-focused values are primarily concerned with what one wants for beings and things outside of that. (It is possible to frame this in a slightly different way without mentioning the complexities of identities larger or smaller than one's self).
Inculturation takes place in many forms, with different ways of affecting the value system of those recieving the inculturation. As noted above, parents play a strong role in inculturation. Initially this takes place through punishment for transgression of their simplest value conclusions, creating through example (much as children acquire language) the particulars from which a "universal" can be synthesised (universal in that it can be applied to the universals of potential situations one might face, not universal in the sense of implying values intrinsically good for all humanity). As a child ages, this is supplemented with direct discussion on these matters. This form of inculturation is commonly percieved as "teaching children the difference between right and wrong" - while this statement is rooted in a value absolutism that is intrinsically flawed, it can be rephrased in better terms as "inculturing children with social values" and it describes an essential activity. Various others find themselves in a position to contribute to inculturation depending on situations - schoolteachers (particularly in old-fashioned schools), other family members, and potentially clergy of various sorts (this list is not exhaustive). The type of inculturation possible changes over time both in origin and style as the inculturated approaches being vested in society. Occasionally people enter situations where they may be inculturated again later in life - entering a new culture or religion often entails making one's value system highly fluid again, allowing one's values to shift markedly until one is vested in a new identity and group.
Inculturation is an essential trait to group membership and an essential process for allowing for personal growth at least in the first instance. As some values are biological in origin, there is no "blank slate" in the field of values for humans, but similarly an uninculturated human is neither capable of civilised behaviour nor finds their natural values sufficient to view the world. Such a theoretical being is both prevented from reaching their potential as a human and likely to clumsily enrich themself in ways quite divergent from the directions other beings in the same state would. A certain similarity of values is necessary for humans to coexist with each other - while the specific common values can be varied, there must be substantial functional similarity on basic issues in ways that permit that coexistence. We might imagine taking 10 highly productive members of radically different societies over the span of human history, placing them together, and finding them to have killed or greatly limited each other over foundational differences in these matters in a short time. Inculturation is the mechanism that prevents this - differences in it is what makes members of the different great civilisations differ from each other (the raising of those of different ethnicities in one's own culture has shown this many times, contrary to claims of many ethnic chauvenists who speak of a "dutch spirit", a "hebrew spark", or "french temperment" - biological differences between races of humans are at most small). Beyond being necessary and defining for civilisation, inculturation is needed to help strengthen other-oriented values - while some of this comes with a natural complexification of notions of identity (e.g. identifying with groups and maturing past simple individualism), without sufficient inculturation and vesting the other-oriented values usually remain too weak to allow for individual or group virtue.
The transition between a period of inculturation and that of being vested is often rough - while some societies offer ceremonies that theoretically act as a delimiter, these traditions often outlive the time when that transition was located at that point in life and perpetuate social confusion. The desire for the respect (and privileges that often accompany vestment) naturally create resentment among many of those who do not have it yet - in order to protect society's values, it is important to maintain the system regardless of complaints and inclinations towards rebellion of those not yet vested in order to hold society together and retain the benefits of a virtuous people (even if in the end they don't all hold the same notions or particulars of virtue). Whatever combination of nurturing and restraining proves effective at building virtue in those not yet vested is to be deemed positive, even in societies that have fuzzy or ill-placed delimiters between the vested and the not.