1. Relative Pronouns
Qui, que

2. Qui Qui can function as a subject or as an indirect object (person)
Translations: who, what, which, that, whom

3. Qui = who or that
Qui is used when the noun replaced is in the position of the grammatical subject. Note that qui -- unlike que -- does not contract before a vowel sound.
Exemples:
J'ai lu un roman qui m'a beaucoup amuse.
J'ai trouvé un appartement qui a trois pièces.

4. Que Que functions as a direct object
Translations: whom, what, which, that

5. Que = that or which
Que is used when the noun replaced is in the position of the grammatical direct object. Note that que will contract to qu' before a vowel sound.
Il a commandé une boisson qu'il n'a pas bue.
Elle parle du voyage que nous allons faire.

6. dont Function: object of de Indicates possession
Translations: of which, from which, that whose

7. Dont = whose or of which
Dont is generally used when the noun replaced is an object of the preposition de. It is commonly used with verbs followed by de such as avoir besoin de, parler de, envie de …
as well as to show possession (similar to whose in English)
Voici le livre dont je t'ai parlé.

8. Lequel/laquelle Functions as an indirect object (thing)
Translations: what, which, that
Lequel or one of its variations replaces an indirect object referring to a thing* after a preposition,** including prepositions which are required after a given verb or expression.

9. Can be used as an interrogative pronoun:
Quel livre veux-tu ? > Lequel veux-tu ?    Which book do you want? > Which one do you want?    Je veux la pomme là-bas. > Laquelle ?    I want the apple over there. > Which one

10. Lequel replaces an inanimate object of a preposition
Lequel replaces an inanimate object of a preposition. (If the object of the preposition is a person, use qui)
Ex: Le livre dans lequel j'ai écrit