Korean verbs change form depending on whom you are speaking to, a system known as speech levels. The four most commonly used are 합쇼체 (hapsyo-che), the formal polite style used in news broadcasts, business, and the military, where verbs end in -습니다 or -ㅂ니다; 해요체 (haeyo-che), the informal polite style used in everyday life, where verbs end in -아/어요; 해체 (hae-che), the casual style used with close friends or younger people; and 해라체 (hara-che), the plain or written style used in narration. 반말 (banmal) refers collectively to casual speech and is reserved for intimates or those younger than you. As a rule of thumb, use formal or polite speech with strangers, elders, superiors, and in any formal setting.
Korean sentences rely on small particles attached to nouns to indicate their grammatical role. The topic marker 은/는 (은 after a consonant, 는 after a vowel) signals what the sentence is about. The subject marker 이/가 (이 after a consonant, 가 after a vowel) marks the grammatical subject of an action. The object marker 을/를 (을 after a consonant, 를 after a vowel) marks the direct object. The particle 에 indicates a static location or a point in time — "at," "in," or "on" — while 에서 marks the location where an action takes place, or signals a starting point ("from"). 의 indicates possession, much like the English "'s" (as in 나의, "my"), and 도 means "also" or "too," replacing the topic or subject marker entirely (so 저도 means "me too").