To someone: 한테, 에게, 께

에게 and the colloquial 한테 can be used to indicate the person being influenced by an action:

친구에게 편지를 보냈어요.
친구한테 편지를 보냈어요.
I sent a letter to my friend.

is an honorific version:

선생님한테 고마워요라고 말했어요.
선생님 고마워요라고 말했어요.
I said thank you to my teacher.

생일에 여자친구에게 꽃을 주었어요.
I gave flowers to my girlfriend on her birthday.

방금 누구에게 말했어요?
Who were you speaking to just now?

주말마다 부모님 전화를 해요.
I call my parents every weekend.

에게 메시지를 보냈지만 그는 답장이 없었어요.
I sent him a message but he didn’t reply.