Superlative

English

The Superlative of the Greatest Degree is formed differently depending on the length of the adjective.
the + short adjective + est
Mary is the smartest.
My car is the cheapest on the market.

the most + long adjective
Mary is the most intelligent.
His car is the most expensive.

The Superlative of the Lowest Degree is formed as follows:
the least + adjective
Paul is the least active.
Her car is the least expensive of all.

Spanish


The Superlative of the Greatest Degree is formed as follows:
el, la, los or las (depending on the gender and the number of the noun described) + más (most) + adjective
Juan es el más bajo de la famila.
John is the shortest in the family.

María es la más alta.
Mary is the tallest.

Carlos y Roberto son los más divertidos de la clase.
Carl and Robert are the funniest in the class.

Teresa y Gloria son las más inteligentes.
Teresa and Gloria are the most intelligent.

The Superlative of the Lowest Degree is formed as follows:
el, la, los or las (depending on the gender and the number of the noun described) + menos (least) + adjective
Mi coche es el menos caro.
My car is the least expensive.

IMPORTANT

Some adjectives in English and in Spanish do not follow the above rule.  For example:

Adjective: Esta manzana es buena.
                This apple is good.

Comparative: Esta manzana es mejor.
                     This apple is better.

Superlative: Esta manzana es la mejor.
                  This apple is the best.