Selected reading on the Internet.
Questions and help
Unix & Linux Stack Exchange is a question and answer site for users of GNU/Linux. This site is all about getting answers.
Ask Ubuntu is a question and answer site for Ubuntu users. Even for users of different distributions of GNU/Linux this can be a helpful resource for finding answers.
Learn and read more
The Free Software Foundation defends and advocates the very concept of free software that gave birth to GNU/Linux.
Note: these links are proposed as a recommendation. They are not commercial.