The Linux kernel is one of most complex open source projects. Even though there are a lot of books on the Linux kernel, it is still a difficult subject to comprehend. The Interactive Linux kernel map gives you a top-down view of the kernel. You can see the most important layers, functionalities, modules, functions, and calls. Each function on the map is a link to its source code. The map is interactive. You can zoom in and drag around to see details.


Source: Interactive Kernel Map

^ Unless you're planning on writing kernel (usually lower level) applications, you generally don't need to bother with the details of the kernel (or even knowing about it at all).