This is actually a super useful particle that you’ve already been using without knowing it! The 시 particle shows up in 안녕하세요, with the literal breakdown of it being 안녕 meaning peace and 하세요 (하다 + 시 + 해요체 honorific form)
When to Use ~(으)시?
The 시 or ~(으)시 particle is only used in formal relationships. So it could be with a boss, teacher, parent, etc. or just people older than you. If you’re new to Korean honorifics, or just need a refresher than check out my post breaking it down here; with shows which to use depending on the situation and nice clear image breakdowns of honorific usage based on age.