How is an OS bound to the Linux kernel

["Gideon D'souza" <gidisrael@gmail.com>]

hey guys,

I generally manage to understand the various pieces of the linux
kernel and what their functions are.

However, one thing I don't fully understand is how is any OS, say
fedora (which is what I use) is bound to the kernel.

Lets say I want to just build a system on top of linux that boots and
keeps printing hello world to the screen. When the user presses a key
it exits.

How would I begin to do this? What should I read or look at?

I'm guessing it's a two part thing right, one I need to somehow tell
the kernel what to do after booting, and second I'll have to tell the
kernel what the screen is ? Where would I find more information about
this?

Note: I actually want to make the program I described so tips on how
to play with grub to get the whole thing to work would also be
helpful.

Regards,
Gideon