person/animal + 에게 (친구에게) · honorific: 께 (선생님께)
to (a person or animal)
Example
저는 어머니에게 편지를 썼어요.
I wrote a letter to my mother.
Word parts
Polite/written; 한테 is the casual version. 친구에게 = to a friend.
Good to know
For places or things use 에; for people and animals use 에게/한테.