Hey there! Nabanna is a word from a language called Bengali, and it means "new banyan tree." But don't worry, we're not talking about a real tree!
Nabanna is actually a big building in the city of Kolkata, in the country of India. It's a very important building because it's where the government of the state of West Bengal works.
Just like how your parents might go to work in an office building, the people who run the state of West Bengal go to work in Nabanna. There are many offices inside, and people work there to make decisions and take care of things like roads, schools, hospitals, and more.
Sometimes, important people like the Chief Minister of West Bengal also work in Nabanna. They have their own special offices inside.
So, in summary, Nabanna is a big building where the government of West Bengal works. It's named after a banyan tree, but it's not actually a tree! It's an office building.