You can still pay for Linux. Well yes it is free, but when you buy it the CD it comes on isn't. Linux is still growing. This isn't so much a bad thing, but it is a shame that it is not supported more. Permission to copy in any medium is granted provided this copyright notice is preserved.
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Kernel - the core of Linux. Imagine it as one large file which is essentially the configuration of your computer. It is compiled when you first install Linux to it's default settings, but with a little tweaking you can customise it to support all the devices on your system. It is when you want to use Linux with devices like sound cards, and scanners that you must recompile the kernel with support for these devices. Basically root has the power of vito over everything on the system.