Default [Q] How can CWM be built in a kernel?

I was learning about android, bootloader etc in xda wiki and I read somewhere that the recovery has its own kernel, so it can load even when the firmware is damaged. Ok, but then i read that some custom kernels have CWM built-in. How can a kernel and a recovery be built in another kernel?

Sorry if I expressed it badly or misunderstood something.
And sorry for my bad english, I'm brazilian.