The Superlative is the form of an adjective or adverb that shows which thing has that quality above or below the level of the others. There must be three or more to use the superlative. It takes the definite article and short adjectives add -est and longer ones take 'most':

SUPERLATIVE EXAMPLES:

Mount Everest is the highest mountain in the world.
It is the most expensive restaurant I've ever been to.

Fonte:

http://www.usingenglish.com/glossary/superlative.html (Com outros links e quiz)

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Comparative:

The Comparative is the form of an adjective or adverb used to compare two things. To create a comparative, remember that with short adjectives add -er to the end, and longer ones use more before the adjective:

EG: The Nile is longer than the Amazon. - Long >> Longer
EG: Many students find writing more difficult than reading. - Difficult >> More Difficult