Qui, que, où

A relative pronoun joins extra information to a noun. Pick it by the job it does in the second clause:

• qui is the subject: a verb follows it directly. La femme qui parle est ma tante (The woman who is talking is my aunt).
• que is the direct object: it is followed by its own subject. Le livre que je lis (the book I'm reading). Before a vowel it becomes qu'.
• où stands for a place or a moment: la ville où je vis (the town where I live), le jour où nous nous sommes rencontrés (the day we met).

Qui and que work for people and things alike. Quick test: no subject after the gap, use qui; a subject is there but the verb lacks its object, use que. For time, French says le jour où, never le jour que.