Dextrose (500 Grams) is used for priming or to increase alcohol content of your beer. Adds very little flavor and can be used in virtually any beer.
As a priming agent, use a about 30 Grams of Dextrose for every US Gallon of beer for medium carbonation.
To Increase the alcohol content of your beer, simply add the dextrose towards the end of your wort boil. Make sure your yeast has high attenuation property like 'Danstar Belle Saison'