There are several ways to make an adverb in Korean.
Generally, the most common way is to conjugate the adjective with the ending ‘게’, but other words may conjugate with ‘히’, ‘이’, or ‘으로’, depending on the verb.
DV + 게
1. ‘게’ is the most common way of making an adverb. You just take a descriptive verb (adjective), remove the stem, and append 게.
맛있게 먹어요! – Eat deliciously!
안전하게 걸으세요! – Walk safely!
DV + 히/이
2. ‘히’ and ‘이’ appear sometimes, but not as often. It depends on the verb, as some verbs use ‘히’ and ‘이’ endings much more naturally than ‘게’.
천천히 말해주세요! – Speak slowly!
한국어 많이 들었어요. – I heard a lot of Korean.
N + 적 + 으로
3. ‘으로’ is only used with a specific set of adjectives. Mainly, those that end in ‘적’. Attaching ‘적’ is equivalent to adding ‘-ness’ to a noun, and appending ‘으로’ to that makes it an adverb.
일반 (general) + 적 (general-ness) + 으로 = Generally
사적 (personal) 으로 = Personally
기본 (basic) + 적 (basic-ness) + 으로 = Basically