Грамматика русского языка. Часть 12. Наречия. Глава 2. Сравнительная и превосходная степень наречий. Russian Grammar. Part 12. Adverbs. Unit 2. Comparative and Superlative Forms of Adverbs.

Adverbs, like adjectives, have comparative and superlative forms (e.g. he runs more quickly and he runs the most quickly).

(a) The comparative adverb is identical to the short form comparative adjective: so, for example: быстрее, more quickly, медленнee, more slowly, лучше, better:

Он всегда работает быстрее, чем я.
He always works more quickly thаn I do.

Adverbs ending in -и form their comparative with более:

Он всегда работает более логически, чем я.
He always works more logically than I do.

Грамматика русского языка. Часть 7. Имя прилагательное. Глава 14. Превосходная степень. Russian Grammar. Part 7. The Adjective. Unit 14. The Superlative.

lf we say something is the most interesting, smallest, best we are using the superlative form of the adiective.
The superlative is very easy to form. Simply put the adjective самый in front of the the adjective and noun you are describing. There is no short form of the superlative (so it can be used predicatively and attributively - before or after the noun):

Самый серьёзный фильм   (the most serious film)
Этот фильм самый серьёзный   (this film is the most serious)

Make sure that the adjective самый agrees in number, gender and case with its adjective and noun:

Я изучаю самый красивый язык   (I am studying the most beautiful language)
Я читаю самую серьёзную книгу   (I am reading the most serious book)
Мы живём в самом приятном районе   (We leave in the pleasantest region)