Polish nouns are listed in the dictionary in the nominative singular masculine form. Most of these end with -y. Some end with -i. Such adjectives never lose the i in declensions.
Like nouns, adjectives decline according to number, case, and gender.
On jest miły (He is nice). Adjective in the nominative singular masculine form.
Ona jest piękna (She is beautiful). Adjective in the nominative singular feminine form.
Kocham tego przystojnego faceta (I love this handsome guy). Adjective in the accusative singular masculine form.
Nienawidzę podłych ludzi (I hate mean people). Adjective in the genitive plural form.
Like in English, Polish adjectives are usually placed before the noun they are modifying. But, if the adjective designates the type of a noun, rather than some characteristic, the adjective often follows the noun.
This is talking about any bear that lives in the polar; not necessarily any specific species or type.
This is talking about a specific type/species of bears; the polar bear. That is why this adjective follows the nouns.