The author can very well imagine that you might have wondered where the declination starts. It is clear that comparatives and superlatives are not declined when used as adverb (because it is invariable) or as predicative.
They are only declined when used as attribute.
Comparatives and superlatives are are declined the same way like adjectives with article or with possessive pronoun. This is because attributie adjectives always use an article or a possessive pronoun. For more details please check the chapter Adjectives.