Superlative adjectives are used to describe something at an upper or a lower limit of a quality and it describes a comparison between a subject and a group of objects.
When the adjective consists of 1 or 2 syllables, it gets -est at the end. 'Most' is added before the adjective when it consists of more than 3 syllables. When the adjective ends on 'y', it changes in 'i' and get -est at the end.
There are irregular forms of adjectives which you could find below in the table.