We use the superlative degree of adjectives to compare three or more persons, places or things.

1. To form the superlative of most adjectives of one syllable and adjectives of two syllables ending in Y, R, W, or LE, we add EST. Note these examples: fast-the fastest, tall-the tallest, lovely-the loveliest, clever-the cleverest, shallow-the shallowest, simple-the simplest.
Bob is the tallest boy in the class.

2. To form the superlative of adjectives of two or more syllables (with the exception of the above mentioned adjectives), we put MOST before the adjective. Note these examples: important-the most important, interesting-the most interesting, economical-the most economical, demanding-the most demanding.
This car is the most economical of the three.

3. Some adjectives have irregular forms in the superlative. Note these examples: good-the best, bad-the worst, many and much-the most, little-the least.
This is the best book I've ever read.