In the superlative you talk about one thing only and how it is the best, worst, etc.
You do not compare two things. The following guidelines apply to the superlative:
Adjectives with one syllable:
1-syllable adjectives: add -est to the adjective (plus the)
My sister is the tallest in our family.
Yesterday was the coldest day of the year so far.
Note: If the word ends: consonant-vowel-consonant, then the last consonant is usually doubled in the superlative.
big - biggest, fat - fattest, hot - hottest
Adjectives of two syllables ending in -y:
2-syllable adjectives ending in -y: change the -y to -iest (plus the)
The richest people are not always the happiest.
Which do you think is the easiest language to learn?
She's the luckiest person I know.
Beware: Do not confuse adjectives and adverbs.
2-syllable adverbs ending in -y form their superlative with the words the most.
Of all the people I know my father drives the most quickly (quickliest).