An indirect object is introduced by à in French, it's the person something is given, said, or done to. Verbs like parler à, téléphoner à, donner à, écrire à all take one.
1. The pronouns
| me (m') | to me |
| te (t') | to you (informal) |
| lui | to him, to her |
| nous | to us |
| vous | to you (formal/plural) |
| leur | to them |
Just like direct object pronouns, these go right before the conjugated verb (or the infinitive they depend on).
| Je parle à Marc. → Je lui parle. | I'm talking to him. |
| Elle téléphone à ses parents. → Elle leur téléphone. | She's calling her parents. |
| Il donne un cadeau à Marie. → Il lui donne un cadeau. | He's giving her a gift. |
2. Watch out: lui and leur don't reveal gender
Same trap as son/sa/ses: lui means "to him" or "to her," and leur means "to them" regardless of gender. Je lui parle could be about a man or a woman, only context tells you which.
3. Exception: penser à and ressembler à
A handful of verbs with à (penser à to think about, ressembler à to resemble, faire attention à to pay attention to) don't use lui/leur at all. They keep à and use a stressed pronoun instead (moi, toi, lui, elle, nous, vous, eux, elles).
| Je pense à lui. | I'm thinking about him. (not "je lui pense") |
| Elle ressemble à sa mère. → Elle ressemble à elle. | She resembles her. |
4. Quick reference
| me, te, lui, nous, vous, leur | right before the conjugated verb (or the infinitive) |
| lui / leur | no gender info, context tells you who |
| penser à, ressembler à | keep à + stressed pronoun (moi, toi, lui...) |