The French superlative is built from the comparative by adding the appropriate definite article: le plus grand (the tallest), la plus belle (the most beautiful), les plus intéressants (the most interesting). The article agrees with the noun, and if the adjective normally follows the noun, the whole superlative phrase follows it too: c'est la ville la plus visitée de France (it's the most visited city in France).
As with the comparative, bon and bien are irregular: le meilleur / la meilleure (the best, for nouns) and le mieux (the best, for verbs) — c'est le meilleur restaurant du quartier, but c'est lui qui chante le mieux (he's the one who sings the best).