How to recover Grub2 in Linux

The grub is the boot, is what allows us to choose between different operating systems to turn on the pc. But we fucked for example every time we install windows and it's really annoying that happens, nothing is more annoying than turning on the pc and it will not boot. But the truth is easy recover grub and all I need is a live cd of Ubuntu (or any distro that uses Grub2) and run a few simple