Go to your home folder, open boot, open grub, select menu.lst (plain text file) - double-click to open. This gives a lot of advice and references, all commented-out from the script which (presumably!) controls the boot process.
Also see The Linux Documentation Project at: http://tldp.org/guides.html
- and from that:
see Introduction to Linux - a Hands-on-Guide at: http://tldp.org/LDP/intro-linux/html/index.html
which at Chapter 4 includes The Boot process - with a lot of description of Grub.
Hope this helps!