Learn Polish: Głowa mnie dzisiaj boli.

In Polish, you usually do not use possessive words (like moja for "my") with body parts. Since the sentence includes mnie (me), it is already perfectly clear whose head is hurting!

Why do we use mnie (me) instead of ja (I)?

The verb boleć (to hurt) works a bit differently than in English. The body part is the subject doing the action, and the person feeling the pain is the direct object (using the accusative case). Literally, this sentence means "The head hurts me."

Does that mean the verb boli is matching the head?

Exactly! Because the head (głowa) is the subject doing the hurting, and it's a singular noun, the verb takes the third-person singular form boli (it hurts). If a plural body part was hurting, like your eyes (oczy), you would use the plural verb form: Oczy mnie bolą.

Why isn't mnie at the beginning of the sentence?

In Polish, pronouns like mnie naturally prefer to tuck into the middle of a sentence. You would generally only put Mnie at the very beginning if you wanted to heavily emphasize it, as if to say "My head hurts today (not yours)."