This ending contains the Brotherhood of Steel for Fallout 4, which aims to destroy the Synth loving Railroad Faction as well as the Institute and bring order to the Commonwealth. The Brotherhood thinks that technology is the main cause for most of the world’s problems but ends up using the same technology to achieve their goals against the Railroads and the Institute.
If you intend to support the Brotherhood of Steel, you will have to go against Railroad and the Institute. You are missioned to retrieve a technological program from the Railroad Faction during which you will have to kill everyone who comes in your way, including every Railroad member.
After you have retrieved the resource, report to Captain Kells, you will then proceed to the next phase of the attack, which is going to be executed on the Institute. After retrieving the holotape program, you will work closely with Proctor Ingram and Dr. Li to rebuild Liberty Prime.
This will require you to gather some resource items, which you can consult Dr.Li. These items will help Prime to be awake and working again. The Prime will be ready after you have retrieved the Agitator, which will power the Robot.
This Robot will be the main role-player in the war against the Institute and will dig a big hold in the ground leading towards the Institute and allowing members of the Brotherhood to infiltrate the Institute. After you have completed the Brotherhood of Steel quests, you will be promoted to the Sentinal Rank and will receive a prize of a Jet pack. The Brotherhood aims to bring order to the Commonwealth with the Railroad and Institute destroyed.