permissions

I am reacquainting myself with linux after many years away and having a harder time. I was always under the impression that when you loaded a distro that the name and password you entered made you the administrator, root, superuser, or whatever other name you want to use AND that these were all considered to be the same entity and if not why not. I am on my 2nd distro because that one and this one denied me editing smb.conf.The previous distro denied me ,while i was logged as SU to edit smb.conf because i was not the 'owner' of the file, root was the owner. This distro tells me that the file is read only after invoking su -i and while letting me modify the file denies me saving because it is read only. I am up to my eyeballs with this permissions nonsense