Okay kiddo, a grivna, also called a hryvnia or гривня in Ukrainian, is a type of money that people use in Ukraine. It's like the dollars or euros that we use here. But instead of having pictures of famous people on it, the grivna has pictures of landmarks and famous buildings in Ukraine.
The grivna is made up of coins and paper bills. The coins are small and round, like pennies and nickels, and they have different values. The paper bills are bigger and have different values too. The higher the number on the bill, the more it's worth.
When people go to Ukraine, they need to exchange their dollars or euros for grivnas. They can do this at a bank or a currency exchange place. Then they can use the grivnas to buy things or pay for services, just like we use our money here.
So, that's what the grivna is, an important type of money used in Ukraine.