Ask HN? Dumb question about the Linux kernel

Hello, I am trying learn about the Linux kernel,

but could not find any documentation on gnu.org or linux.org

Could someone help me demystify the kernel?

Just a brief explanation of it's core ideas would be sufficient.

I am only interested in that kernel

and not its comparative analysis relative to mach or some of the other later kernels.

This is likely a tough question to answer

since most of the guys on this newsgroup are probably not very familiar with such dated concepts.

Thanks.