Linux - Set folder & File permission inheritance on sub-folders and files

We are a Linux file server.
I have created a new folder and get a group ownership to that folder. I have given the specific user access to that group.
When a use creates a file or folder it make it read only for all other users.
How can I set it so that any file and sub folder will still retain the same permissions as the parent folder?
I will then also need to run a command that will change all permissions on the all curenly folders already created.