Ok, so if you imagine a big map of a country, like a puzzle, there are different pieces that make up the whole picture. And sometimes, some of those pieces have special names because they are different or important in some way.
Korosten is one of those special pieces, it's a place in Ukraine, which is a country in Europe. Just like how your house has a name or address, Korosten is the name of a town in Ukraine.
People have been living in Korosten for a long, long time, even before your grandparents' grandparents were born! They have a lot of history there, like stories and things that happened in the past.
There are also important things in Korosten called monuments, which are like big statues or buildings that show something special or important about the history of the town. People can visit Korosten to learn about the history and see these monuments.
So, in summary, Korosten is a special place in Ukraine with a big history and important things to see and learn about.