Concerts and fireworks mark the day that, in 1998, Ukraine adopted its constitution, which made it a semi-presidential republic.
For decades Ukraine was part of the Soviet Union, which was dominated by Russia. Today the Ukrainian language, which is the official language, is supplemented by most speakers also knowing Russian. In some areas, Russian is more common, especially in the cities.
Ukraine is the largest country in Europe, and it's famous for its Easter eggs, called pysanky, and (unhappily) for the nuclear disaster in Chernobyl. There are lots of beautiful buildings to see in Urkaine, as you can see here and on this travel site.