Just like だ, です is an auxiliary verb that expresses determination or assertion. It conveys that something 'is' in a particular manner. です is regarded as the polite form of だ. However, it's important to note that while their functions are alike, both だ and です can stand alone. です links to words in the same manner as だ, but is also frequently found at the end of い-Adjectives.
だ should never be attached to the end of い-Adjectives. In these cases, it is considered more correct to attach a polite equivalent, like です.