St George's Day in England remembers St George, England's patron saint. The anniversary of his death, which is on April 23, is seen as England's national day. According to legend, he was a soldier in the Roman army who killed a dragon and saved a princess.
I think it depends where you live. In my town it's usually a parade with local marching band etc. while in the nearby market town they put a pageant on with George and the Dragon doing battle.