The part nobody shows you
Before your operating system exists, something wakes the processor, sets up the memory and finds a disk. That is the boot firmware — the first code a computer runs. On almost every machine sold it is a binary you cannot read or replace, and it decides what runs next. Libreboot replaces it with code you can read, build and flash yourself. Everything above it stays the same: the same Linux, the same tools, the same disks. What changes is that the first thing to run is no longer a secret.