Very often we imagine culture as something passed on from one generation to the next. It is easy enough to construe this as if culture resides in an individual and is passed on to that individual's children. However, while culture is expressed in and enacted by the individual, it also has a source outside the individual, namely the cultural group itself.
Some groups, like churches and schools - or even gangs - may have privileged individuals who are expected to take the lead in teaching the group's values to new members, while other members are expected simply to enact their roles appropriately. Some groups do not.
Sports culture is one that I've been considering lately. I can't tell you how much I've learned about sports since meeting my husband, who as an Aussie seems to have a limitless interest in sports and the statistics thereof. What I've found is that by picking up some of the culture's relevant terms, such as a sense of which scoring structure belongs to which sport, I can have more interesting random conversations with guys. Fortunately my husband encourages this. I think in a way it keeps that area of his life from being boring and unreachable to me. I guess you could say that the sportscasters function as the privileged individuals in this group, teaching terminology etc. Even the idiosyncratic expressions (boo-yah, anyone?) of particular individuals can get picked up by the group and become part of the local lexicon. This is also a group that encourages the use of puns that might make others scream. While it forms a part of male culture, it is not exclusively male; I'd say it forms an intersection with the male group.
The other one I'm thinking about is child culture. This is the one that blows my mind currently. I'm talking not about things that teachers teach to kids, but the things that children teach to each other. Little rhymes and songs can take on a life of their own, passed from child to child on the playground and thereby staying alive for years, hardly noticed by the adults all around. I find myself hearing my son say things I remember from my own childhood, but never taught him - and it occurs to me that so long as the playground talk stays alive, and the repetition continues there, why shouldn't a particular rhyme stick around for thirty years?
Subcultures like these have their own language patterns, so don't forget to consider what subcultures might exist in your worlds. While you're at it, consider that a culture can even deliberately change their language - witness the revival of Hebrew to a living language by the people of Israel. Language is a badge of membership in a culture, and also in subcultures.
So to answer the question I started with, culture is inside us, and it's outside us. We enact it, we mark ourselves by enacting it, and in enacting it, we take part in its processes of change. Those guys in business aren't wrong when they talk about the "culture of an organization." Neither are we wrong when we talk about "my culture."
Come to think of it, we all have multiple cultures within us - and if those cultures come into conflict, as when we must deal simultaneously with representatives from two different subcultures in our lives, that's when things get interesting.