File:/etc/apt/sources.list
deb http://raspbian.raspberrypi.org/raspbian/ bullseye main contrib non-free rpi
deb http://archive.raspberrypi.org/debian/ bullseye main
deb http://deb.debian.org/debian bullseye main contrib non-free
deb http://security.debian.org/debian-security bullseye-security main contrib non-free
deb http://deb.debian.org/debian bullseye-updates main contrib non-free
The raspbian repository is the majority of the software that is used on the Pi. It is basically the Debian armhf release recompiled to run on the ARMv6 that is used on the Pi 1 and 0. (with a few tweaks to improve performance). Debian armhf won't work on a Pi 1 or 0 as they only support ARMv7 and later.
The archive.raspberrypi.org repository contains code produced by or modified by Raspberry Pi Trading. It contains Pi specific code to take full advantage of the hardware of the Pi. In there you will find the Linux Kernel, the "firmware"/bootloader code, enhanced versions of VLC and Chromium Browser and more specifically for the Raspberry Pi.