The "Izz al-Din al-Qassam Brigades" are a group of people who are part of a larger organization called Hamas, which is a political and militant group in Palestine. They are named after a man named Izz al-Din al-Qassam, who was a Palestinian preacher and fighter in the 1930s.
Think of Hamas like a club, and the Brigades are like the special group of people within the club who are in charge of fighting and defending their club. The Brigades are the armed wing of Hamas, and they carry out attacks on Israel and other enemies of Hamas.
Their activities are controversial and violent, and they are considered a terrorist organization by many countries, including the United States. The group believes in using violence and force to achieve their goals, which include the liberation of Palestine from Israeli occupation.
In simpler terms, the Izz al-Din al-Qassam Brigades are a group of people who use violence to fight against Israel and other enemies of their political group, Hamas. They believe in using force to achieve their goals, but their actions are considered controversial and violent by many people.