Two types of systems exist - distinguished by how the system initializes hardware components and how the system boots.
It is important to know that UEFI based systems is different when you install the bootloader and you should not mix MBR and UEFI.
This document is about modern UEFI based systems. If you have an old BIOS based system don't use this document.
This can be either
And you should not mix the two - it will only lead to trouble.