The White Russian is a sweet cocktail for many occasions. It was the favourite drink of 'The Dude' in The Big Lebowski.
Recipe:
Mix the Kahlua and vodka (preferably on ice) and top with milk or cream.
A Black Russian is basically a White Russian without the cream.
see also the Wikipedia Cocktail Guide
White Russia is Belarus; Black Russia[?] is a name for central and southern Russia. These place names have little if anything to do with the drinks.