1. CentOS help channels:
Forums: 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.
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
Info pages: At the console, you can view an information page by doing 'info
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.