le comparatif et le superlatif des adverbes

comparative of adverbs: indicating more, less, or equality

Plus + adverb + que conveys the idea of 'more ... than'.

moins + adverb + que the idea of 'less ... than'. 

Aussi + adverb + que conveys the idea of 'as ... as.'

Note that mieux (better) is the irregular comparative form of the adverb bien (well). The other comparative forms of bien

are regular (moins bien que, aussi bien que).

superlative of adverbs: indicating the most, the least

In French as in English, the superlative is a way to express a maximum  or minimum  quality  or capacity: 'the fastest', 'the least fast'. 

formation:

To form the superlative of an adverb,  the masculine  singular form of the definite  article is always used: le, followed by plus (more) or moins (less)  before the adverb. Note that the superlative of an adverb  has only one form.  

Le mieux (the best) and le moins bien (the least well) are the superlative forms of the adverb bien (well).