as a noun, 'best' refers to the most excellent or desirable type or quality.
She is the best of the two players.
The best is yet to come.
At his best, he is an excellent performer.
When used as a noun, 'best' often appears in the phrase 'the best of' to specify what it is being compared to.
as an adjective, 'best' is the superlative form of 'good,' and it is used to describe something that is of the highest quality, excellence, or suitability among three or more entities.
She is the best student in the class.
This is the best book I've ever read.
The best way to learn is by doing.
'Best' is irregular; do not use it as 'most good.' Avoid using 'best' to compare only two things; for that, the word 'better' is appropriate.
As an adverb, 'best' modifies a verb, adjective, or another adverb to indicate that something is done in the most excellent or effective manner possible.
She sings best.
He runs best when he's relaxed.
You learn best by doing.
When used as an adverb, 'best' usually doesn't require 'the,' but the comparison is usually understood.