to get good answers you need to ask better questions.

read on LFS site (link below) to get a fairly detailed explanation how a Linux system boots.

http://www.linuxfromscratch.org/lfs/
start looking here (just read any of them, they are fairly similar, i would suggest this to begin with.
http://www.linuxfromscratch.org/lfs/view/stable/
then do a google search or two, this is a subject that can occupy a few meters of shelfspace.

and YES there is a linux Kernel and what else needed to boot on the CD or DVD, you can remove the HDD and it will still boot just fine.
no it does NOT use anything of the other OS.
however it DOES use prom information on motherboard, NIC... and to some extent BIOS.
EDIT
look here aswell
http://oldfield.wattle.id.au/luv/boot.html
/EDIT