Kvass is a traditional fermented Slavic and Baltic beverage commonly made from rye bread, which is known in many Central and Eastern European and Asian countries as "black bread". The colour of the bread used contributes to the colour of the resulting drink.
Ground coffee is what brewed coffee is made of. It's made up of ground coffee beans, much like flour is made of wheat and maize is made of corn. You use ground coffee like you would use a tea bag: add hot water to it, let it steep for a few minutes, then strain and drink.