Learn French: Il a mis sa main sur sa joue. - He put his hand on his cheek.

In French, possessive adjectives like sa agree with the gender of the item being owned, not the person who owns it. Both main (hand) and joue (cheek) are feminine nouns, so we use the feminine sa even though the owner is a man (Il).

Could sa main sur sa joue also mean her hand on her cheek?

Yes! Because sa just tells us that the hand and cheek are feminine, it does not tell us the gender of the owner. Out of context, sa main can mean his hand or her hand. We only know it means his here because the sentence starts with Il (he).

I learned that French usually uses words like le or la for body parts. Why use sa here?

You are right that French normally uses the definite article (le, la, les) for body parts when the owner is obvious, especially with reflexive verbs like il se lave les mains (he washes his hands). However, we often use possessive adjectives like sa for body parts when describing a specific pose, gesture, or physical interaction to make the sentence sound natural and clear.

What verb is mis from, and how is the past tense formed here?