Okay kiddo, so the Mahavamsa is a very old book that tells the story of Sri Lanka. It was written a long, long time ago by some very smart people who wanted to document the history of their country.
The book starts at the very beginning, when a big, strong man named Vijaya came to the island and started a kingdom. It then goes on to talk about all the kings and queens who ruled throughout the years, and all the battles and wars that happened.
But the book isn't just about wars and battles, it also talks about how Buddhism came to Sri Lanka and how it spread throughout the country. The Mahavamsa tells the story of a Buddhist monk named Mahinda who came to Sri Lanka and taught people about Buddhism.
The Mahavamsa is a very important book because it helps us understand the history and culture of Sri Lanka. It tells us how people lived in the past and how things have changed over time. Even though it was written a long, long time ago, we can still learn a lot from it today.