When you compare two people or things, use the comparative form of the adjective.
Lots of comparative adjectives end in -er.
Use the superlative form of an adjective to compare three or more nouns. Lots of superlatives end in -est.
clean cleaner cleanest
easy easier easiest
fat fatter fattest
flat flatter flattest
heavy heavier heaviest
With some adjectives, you use more to make the comparative form, and most to make the superlative form.
active more active most active
charming more charming most charming
cheerful more cheerful most cheerful
The comparative and superlative forms of some adjectives are completely different words.
bad worse worst
few less least
many more most
much more most
Kaynak: Basic English Grammer Book1