Korean Grammar: Stem(어간) and Ending)(어미) 

Let's study the sentence, “안녕하세요, 오늘 날씨가 정말 좋네요.” The base form of "안녕하세요" is "안녕하다". Korean verbs and adjectives are formed by combining a word's stem and an ending. Unlike English adjectives, Korean adjectives have a descriptive function similar to verbs. In Korean, "안녕하세요" is an adjective.
The "안녕하-" in "안녕하세요" is the stem, which is the part that doesn't change when the adjective is conjugated. In "안녕하세요," "-세요" is an interrogative ending of ordinary honorifics as 안녕하세요 is asking the other person's status politely.
"가" in "날씨가" is a subjective particle that tells us that the weather is the subject of the sentence.
The base form of "좋네요" is "좋다." The stem of 좋네요 is "좋," and "네요" is an exclamatory sentence final ending. The final ending of exclamatory sentences in Korean is 감탄형 종결어미, and the interrogative ending of ordinary honorifics is 예사 높임의 의문형 종결 어미.