On any NTFS volume, access to a folder is controlled by the security tab in the folder's properties.
Any particular folder you have in mind?
Don't fiddle with system folder's security.
If you create a new folder in the root of C:\ and give it a name (whatever you want to call it), right click it and choose properties and then the Security tab, use the advanced button to "Disable inheritance" as there will always be permissions to new folders that are cascaded down from the parent.
At that point you can remove all inherited permissions and add the users or groups you specifically want added and the level of access you want them to have.
As I've already said, don't fiddle with folders that are part of the OS.