Shared folders with permissions

Dear Admin,

please, i just bought a new ReadyNas 3130 for my company. i have configured users with password. i have als configured group account. i assigned users to the each groups and it all works fine. i also configured shared folders and users were able to access them with user right access and permissions. the challange i have now is, from the sub folders i want to grant permission to specific users. i.e. User A should have access to folder B. user C should be denied access to Folder B and so on.

please, help me out.

Thanks.