The national Brazilian soft drink. Guarana (and Diet Guarana, should you be so interested) is a sweet, carbonated, caffeine free beverage available throughout Brazil. It is sold by several bottling companies, some of them domestic Brazilian and some the usual international monster conglomerates such as Coca-Cola and PepsiCo.
Guarana is less acidic than Coke or Pepsi and has a fruity taste. The appearance is somewhat golden in color and if one were careless enough it could be mistaken for beer. Guarana soda may or may not contain actual Guarana berry extract, although if it does I personally doubt that it contains very much. It's cheaper and more sterile to just use artificial flavoring.
A final point. Guarana, despite ending in 'a', is grammatically masculine. It is proper to say "um Guarana" but not "uma Guarana." Don't ask me why.