Use the comparative degree when you are comparing two people, things, or actions.
Use the superlative degree when you are comparing more than two. The superlative degree puts the modified word over all the others in its group.
Most one‐syllable and some two‐syllable adjectives form the comparative and superlative degrees by adding ‐er or ‐est: tall, taller, tallest; smart, smarter, smartest. The adjective's final consonant is sometimes doubled: big, bigger, biggest; sad, sadder, saddest. A final ‐y is changed to ‐i: dry, drier, driest; happy, happier, happiest. There are a few exceptions: good, better, best; bad, worse, worst. If an adjective has two or more syllables, it usually forms the comparative and superlative degrees with more and most: more intelligent, most intelligent; more difficult, most difficult.
Most adverbs form the comparative and superlative forms with more and most: more slowly, most slowly; more gracefully, most gracefully; more quickly, most quickly. There are a few exceptions: hard, harder, hardest; fast, faster, fastest; soon, sooner, soonest.
Be careful not to double comparative degrees: funny, funnier (not more funnier) , funniest (not most funniest). Do not use the ‐er or ‐est forms with more or most. Whenever you aren't sure about how to form the comparative and superlative of a particular adjective or adverb, check a dictionary.