To form the superlative, place the definite article before the noun being compared. Follow the noun with más(more) or menos(less), then the adjective and finally de.
definite article
+ noun
+ más/menos
+ adjective
+ de
EXAMPLES:
Es el edificio más alto del mundo. It is the tallest building in the world.
Marta es la chica más alta de la clase. Marta is the tallest girl in the class.
Attention: Note that after a superlative the Spanish de translates to the English in.