Most grub documentation is difficult for those not familiar with grub. Grub from the ground up is different.
It starts by discussing the relationships between the partition containing the kernel (the grub root partition), the partition containing /sbin/init (the Linux root partition), and the grub commands to boot based on those partitions, the kernel filename and location, and possibly the initrd filename and location.
It guides the reader through making a simple grub floppy capable of booting a Linux box, and using that floppy to bust back into a locked system. It then guides the reader in making a grub boot floppy with separate stage1 and stage2 files, and using that floppy to install a minimal grub bootloader on a Linux system, even if that system never had grub before.
Finally, it reveals some tricks and tips for a system with grub installed, including how to make a simple grub menu file.