How do you say this in Korean? Olá

안녕 (informal)
ㅎㅇ (하이) (Slang & Texting, informal / casual)
안녕하세요 (formal / polite)
안녕하십니까 (honorific / very polite)

안녕 is informal or casual used to the same age(friend), someone younger than you, the children, lover
(low formality / low politeness)

안녕하세요 is 세 is honorific + 요 is informal (but still) polite used to strangers(someone you don't know), olders, seniors, teacher, boss, everyone
(low formality / high politeness)

안녕하십니까 is honorific or very polite used to olders, elders, seniors, boss, army, officers, everyone.
(high formality / high politeness)