|FreeBSD Handbook and FAQ|
PC-BSD has FreeBSD as its underlying operating system, so everything in the FreeBSD Handbook and FreeBSD FAQ applies to PC-BSD as well. Both are very comprehensive and cover nearly every task you can accomplish on a FreeBSD system. They are also an excellent resource for learning how things work "under the hood" of your PC-BSD system.
Note: some configurations described in the FreeBSD Handbook already "just work" on your PC-BSD system as they have been pre-configured for you. In these instances, reading that FreeBSD Handbook section can help you to understand how your system was configured and how it works.