Anni di piombo is an Italian term that refers to a period of political violence and social unrest in the late 1960s to the early 1980s. During this time, there were many different groups with different beliefs and goals, but they all used violence as a means of achieving their objectives.
Imagine that there is a big group of kids in your school, and they all have different ideas about what they want to do during recess. Some kids want to play kickball, some kids want to play tag, and some kids want to just sit and read. But some other kids don't agree with these ideas. They want to have complete control over what everyone does during recess and they don't care if other kids get hurt.
These groups of kids then start using violence to get what they want. They bully and beat up other kids who don't agree with them and they damage school property. This makes everybody scared to go to school and ruins the fun of recess.
This is what happened during anni di piombo, only it was with adults instead of kids. There were different political parties and groups with different beliefs about how the country should be run. Some of these groups believed in using violence to achieve their goals, like bombings and kidnappings. This made life very dangerous for everybody in Italy, and many people lived in fear.
Just like how the teachers and principal at your school eventually stepped in to stop the violence, the Italian government eventually took steps to put an end to anni di piombo. However, it took many years and caused a lot of damage and suffering along the way.