Help may be obtained at the following locations:
1. CentOS help channels:
Fora: That's where you are now. Please also read the other documents in this section.
Mailing lists: The CentOS discussion and information list is a general purpose communication list for CentOS and is appropriate for asking questions relating to CentOS.
Wiki: The Wiki has sections containing howtos, FAQs and tips and tricks. The answers to many questions may be found here and the Wiki has a search feature to help you find them.
IRC: You may ask your question on the #centos IRC channel.
FAQs: There are FAQ sections on the main site and Wiki
Documentation: CentOS is provided with extensive documentation, so please read it. Links currently broken. Consult TUV's Documentation.
2. Use the application's help/documentation system
Most all Linux applications come with built in help or documentation.
Help menu: Most all GUI applications have a help menu.
Man pages: At the console, you can view a manual page by doing 'man '. For example, 'man bash' will access the manual page for bash. KDE users may also view man pages in konqueror by typing man:bash, for example, in the location bar.
Info pages: At the console, you can view an information page by doing 'info '. For example, 'info bash' will access the information page for bash.
It should be noted, that for the new Linux user, man pages and other built in help may at first seem quite obscure and/or cryptic. In many instances, these man pages were written by programmers for programmers, but they often contain the answer you seek.
It is more than likely that your question has been asked, and answered, before so please search the above repositories of information before asking. Searching on Google is another highly effective way to obtain answers.
Some books for CentOS users recommended by community members (note: not officially endorsed by the CentOS project).
Fedora and Red Hat Enterprise Linux Bible, Christopher Negus (pub: Wiley). A good reference for both new and more experienced users.
Red Hat Enterprise Linux 6: Desktop and Administration, Richard Petersen (pub. Surfing Turtle Press)
Fedora Linux Toolbox: 1000+ Commands for Fedora, CentOS and Red Hat Power Users, Christopher Negus & Francois Caen (pub: Wiley). Recommended for those wanting to brush up on their command line skills.