Here is a site that I think you will like: ftacademy.org
Specifically, in the materials section, there is a down loadable PDF titled GNU/Linux Basic. I downloaded and have been reading it myself and as a Linux user with several years of experience I have been learning from it. It covers a wide range of topics from how the file system is organized, the fundamentals of the process tree, basic shell commands and how to perform fundamental operations, and more. The site has other 'books' that are freely available too on more advanced subjects and on specific areas of interest too.