sae iusege insahaesseoyo.

new

Breakdown of sae iusege insahaesseoyo.

• ~에게: dative particle
• 이웃: neighbor
• 인사하다: to greet / to say hello

Questions & Answers about sae iusege insahaesseoyo.

Why is there no I or subject in the sentence?

Korean often omits the subject when it’s clear from context.
So (저는) is understood: (저는) 새 이웃에게 인사했어요. = I greeted the new neighbor.
You only add the subject if you need contrast/emphasis: 저는 (as for me), 제가 (I, specifically).

What does 새 do here, and why is it placed before 이웃?

새 is an adjective meaning new, and Korean adjectives typically come before the noun they modify:

• 새 이웃 = new neighbor
  It directly modifies 이웃 as one noun phrase.

What does 에게 mean, and why is it used instead of an object marker like 을/를?

에게 marks the recipient/target (to/for) of an action, especially with people/animals.
With 인사하다 (to greet), Korean usually phrases it as “greet to someone”:

• 이웃에게 인사했어요 = I greeted the neighbor (literally, I did greetings to the neighbor)
  Using 이웃을 인사했어요 sounds unnatural because 인사하다 doesn’t normally take 을/를 for the person.