Learn Hardcore Korean: meoriga apayo.

In Korean, the subject of a sentence takes -가 (after a vowel) or -이 (after a consonant). Here, 머리 (“head”) is the subject experiencing pain, so we attach -가 to mark it as the subject of 아프다 (“to hurt”).

Why don’t we see “I” or “my” in this sentence? How do you say “my head hurts”?

Korean often omits pronouns when the meaning is clear from context. 머리가 아파요 literally means “the head hurts,” but contextually it implies “my head hurts.” If you want to be explicit, add a possessive pronoun:

제 머리가 아파요 (formal)
내 머리가 아파 (casual)

What is 아파요 and how does it relate to 아프다?

아프다 is the dictionary (base) form meaning “to hurt” or “to be in pain.” Conjugated into the polite present tense, it becomes 아파요. Thus, 머리가 아파요 means “the head hurts” in a polite style.

Can 아프다 be used for other body parts?

Yes. You can swap in any body part plus the appropriate subject particle. For example:

배가 아파요 (“my stomach hurts”)
무릎이 아파요 (“my knee hurts”)
치아가 아파요 (“my tooth hurts”)