Larry is right.
I just show the variety of it below.
We tell Grub where you want to source its system files from by the "root" statememnt.
The "setup" is to link the Grub's system files to the location you desire.
We can play tunes with it.
Say if you want Grub in the 14th partition of your 3rd disk to
(1) able to boot from a floppy,
(2) in the MBR of the 1st disk
so that it boots whenever there is no floppy in the drive,
(3) chainloadable in its root partition
so that anther operating system can boot it (like Xp, Vista or another Linux)
(4) put into the MBR of the 3rd disk
just in case you may need it one day
(5) Boot it up now
You can all them in one go in a Grub shell or a Grup prompt. The latter is needed if you want Item (5). A Grub shell is the one you get it in the Linux terminal by typing "grub". A Grub prompt is the one you get by pressing the "c" key at the booting screen at which time the kernel has not yet been loaded. Many distros drop the Grub prompt and offer you a graphic screen instead.
The partition becomes chainloadable after it has been "setup (hd2,13)
What Grub does in the "setup" statement is to dump its stage1 (512 byte large) in the specified destination and hard-codes the hard disk address specified in the "root" statement so that it can get back to it.
There is nothing complicated involved. People just don't play around with a boot loader because it is low-tech.