Culture is world building. That falls to the DM, so talk about Culture would be in the DMG, unless like Pathfinder Player-centric and DM-centric stuff are in one book. For player perspective they can only have any relevant game mechanics the cultures give and offer a few suggestions of different roleplaying ideas. They would have to be told to work with your DM to create a character that works within the gameworld. It is the DM's job to create the world and its cultures. The Game could offer advice and different ideas, but ultimately the DM has to do it if he chooses to run in his own made-up world. The Game can't do the culture work for the DM unless it's A) The one and only permissable world for that particular game system or B) Offer supplemental books each dedicated to a specific world where culture can be developed which can be different than what another supplemental book offers. D&D uses method B. A dwarf in Forgotten Realms is distinctly different than a dwarf in Eberron who is distinctly different than a dwarf in Theros who is distincly different than a dwarf in the homebrew game world of a DM two towns away from where you live. However, they all use the Mountain Dwarf and Hill Dwarf statistics of the PHB.