Compile a linux kernel for run a specific program at start

So I've come up with the idea of starting to create my own Linux build (only for fun) but I'm already stuck.

I know how to compile the Linux kernel (Although I have never done it) but now I can tell the Kernel to start my program on top of it?

p.s. my program it's the following (Only for test presuppose as I've already said)

#include <iostream>using namespace std;int main() {    cout << "Hello World! Hello Universe! Hello All!" << endl;}