In order to install GRUB as your boot loader, you need to first install the GRUB system and utilities under your UNIX-like operating system (see Obtaining and Building GRUB). You can do this either from the source tarball, or as a package for your OS.
After you have done that, you need to install the boot loader on a drive (floppy or hard disk) by using the utility grub-install (see Invoking grub-install) on a UNIX-like OS.
GRUB comes with boot images, which are normally put in the directory /usr/lib/grub/<cpu>-<platform> (for BIOS-based machines /usr/lib/grub/i386-pc). Hereafter, the directory where GRUB images are initially placed (normally /usr/lib/grub/<cpu>-<platform>) will be called the image directory, and the directory where the boot loader needs to find them (usually /boot) will be called the boot directory.