http://www.linux.org http://www.tldp.org http://www.lowfatlinux.com http://www.linuxquestions.org
a kernel is the piece of software that makes the basic parts of your hardware work--->hard drives,ethernet,sound,video,keybrd,mouse, etc etc Windows has a kernel too, only in windows your stuck with what you get, you can have an infinite number of ones in linux, and you can make your own.Much of the actual work for peripherals is done by modules that work with the kernel to make your hardware work(drivers), but they are compiled to work together.
linux in its basic form is a kernel compiled and linked together with the GNU/GPL toolset which forms whats called a toolchain or basic OS, from there software is added so you can do things, almost all of this is written in the C language, its all open source and free
Basically, its an open source version of unix for the desktop PC in whatever architecture you use, x86,PPC, whatever, your not stuck with just intel/AMD, it will even run on an apple PC.It also has ALL the traits of unix, its multiuser, meaning more than one person can be logged in and use the same PC at the same time, and all the protections that come from that type of system are present.
that will give you a small start anyway