Okay kiddo, so the Belfast Brigade was a group of men and women who worked together as part of a larger group called the Irish Republican Army (IRA). They wanted to fight for their rights and to have their own country separate from the United Kingdom.
The Belfast Brigade was made up of people who lived in Belfast, which is a city in Northern Ireland. They did things like collect weapons, plan attacks on the British army, and make propaganda (which is like trying to convince people to support your ideas).
But fighting can be dangerous and scary, and unfortunately many people were hurt or killed during the time that the Belfast Brigade was active.
Nowadays, things are a lot more peaceful and people are working towards finding solutions to problems without violence.