Building ROMs & Kernels?

I've been using customs ROMs and Kernels on my GS5 for a while now, but I want to get a clear explanation about how it works. Here are a few questions: 1. What is 'building' in Android? I heard that the build system is different from other Linux systems. 2. What's the difference between a ROM and a Kernel? 3. Is the 'ROM part' and 'Kernel part' separated? So, can I build them separately and install them separately? 4. How do I add device drivers(such as WiFi dongles) to my Kernel? 5. Inside a custom ROM zip file, is the Kernel included alongside with the ROM? 6. Are kernels compatible with different ROMs? (E.g. Using a Kernel built from the official stock sources on CyanogenMod) These may be very newbie-ish questions but I'm really, really curious.