[CentOS] Permissions

I am trying to figure out how permissions work in Linux. In windows if I want someone to have access to something you put their name in a group then give that group access to that folder. However things can get difficult when you have an office with a folder structure like this: Taxoffice--->Names---> Private. Everyone in the group would need access to the Taxoffice folder and names folder but lets say only 4 people out of 12 need access to the private folder. 2 of those people need read only access and 2 full access. In windows this is easy because you can apply multiple groups and peoples permissions to a folder and file. How is this done in Linux when all I see is Owner and 1 Group permission?