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). There are two ways of doing that - either using the utility grub-install (see Invoking grub-install) on a UNIX-like OS, or by running GRUB itself from a floppy. These are quite similar, however the utility might probe a wrong BIOS drive, so you should be careful.
Also, if you install GRUB on a UNIX-like OS, please make sure that you have an emergency boot disk ready, so that you can rescue your computer if, by any chance, your hard drive becomes unusable (unbootable).
GRUB comes with boot images, which are normally put in the directory /usr/lib/grub/i386-pc. If you do not use grub-install, then you need to copy the files stage1, stage2, and *stage1_5 to the directory /boot/grub, and run the grub-set-default (see Invoking grub-set-default) if you intend to use `default saved' (see default) in your configuration file. Hereafter, the directory where GRUB images are initially placed (normally /usr/lib/grub/i386-pc) will be called the image directory, and the directory where the boot loader needs to find them (usually /boot/grub) will be called the boot directory.