Just like English, Korean verbs conjugate to reflect tense, nuances, etc. Unlike English, however, Korean adjectives also conjugate just like verbs with slightly different rules. For that reason, Korean adjectives are often called “descriptive verbs” in many textbooks for English-speaking students. You can think of Korean adjectives as a combination of a linking verb (is, am, are, was, etc.) and an adjective in English. For example,
날씨가 좋아요. (The weather is nice.)
날씨가 좋았어요. (The weather was nice.)
날씨가 좋을 거예요. (The weather will be nice.)
In that sense, both verbs and adjectives conjugate in Korean.