http://www.dedoimedo.com/computers/grub.html very good explanation on GRUB
To be able to successfully master the secrets of GRUB, you must understand one of the basic foundations of *NIX-based operating systems. Everything is a file. Even hard disks and partitions are treated as files. There is no magic. If you remember this, you will find the supposedly perilous task of tampering with partitions no different than playing with files using a file explorer (or the command line).
Kernel recompile is for your information. We won't be able to recompile in class due to shortage of time. We'll just go over some important points.