Form Ranks Main Story, Minutmen Quest
I should talk to Preston Garvey about how the Minutemen can help me destroy the Institute.
This quest will be triggered or can be aquired when you complete Institutionalized quest.
Stages of "Form Ranks" quest
1. Talk to Preston Garvey about the Institute
2. Recruit more settlements for the Minutemen
The Minutemen are not strong enough yet to take on the Institute. I should work on building up support across the Commonwealth.
You will also receive another quest - Old Guns.
3. Quest completed
The Minutemen are now strong enough that we can think about taking on the Institute.