A clause is a group of words that contains a verb, The clause modifies, or describes the noun.
Une proposition est un groupe de mot organisé autour d’un verbe
A relative pronoun is a type of pronoun used to connect a relative clause to the main clause in a sentence.
Relative clauses either help clarify who or what a sentence is talking about (known as the antecedent), or else give extra information about it.
Here are the five most commonly used relative pronouns:

That, which, who, whom, whose

Functions of the relative pronoun
In a relative clause, the relative pronoun functions in one of three ways: as the subject, the object, or a possessive pronoun
le pronom relatif fonctionne de trois manières: en tant que sujet, complément ou pronom possessif
The usage of a relative pronoun ultimately depends on its antecedent and the relative clause it introduces.
We can use this table as a quick guide:

Let’s look at how each of these can be used in a sentence:
a) Subject ( Sujet )
• The woman who came to my house was a salesperson.
La femme qui est venue chez moi était une vendeuse.
Who is the subject of the relative clause who came to my house, which describes the antecedent the woman.
• The male birds danced and sang, which attracted nearby females.
Les oiseaux mâles dansaient et chantaient, ce qui attirait les femelles à proximité.
Which is the subject of the non-restrictive relative clause which attracted nearby females that describes the antecedent danced and sang.
• I have to go mend the fence that is broken.
Je dois aller réparer la clôture qui est cassée.
That is the subject of the restrictive relative clause that is broken, describing the antecedent the fence.
• I want a computer which can download a lot of games.
Je veux un ordinateur capable de télécharger de nombreux jeux.
Which is the subject of the relative clause which can download a lot of games and describes the antecedent a computer.

b) Object ( Complément )
• I don’t know if I passed the test that I took yesterday.
Je ne sais pas si j’ai réussi le test que j’ai passé hier.
That is the object of relative clause that I took yesterday and describes the antecedent the test.
• The new employee whom I hired is a dedicated worker.
Le nouvel employé que j'ai embauché est un travailleur dévoué.
Whom is the object of the relative clause whom I hired and describes the antecedent the new employee.

c) Possession
The relative pronoun whose is unique in that it is the only one that can describe possession. It comes before a noun in a sentence, modifying it like an adjective to indicate that it belongs to the antecedent.
Le pronom relatif "whose" est unique en ce qu'il est le seul qui puisse décrire la possession. Il vient avant un nom dans une phrase, le modifiant comme un adjectif pour indiquer qu'il appartient à l'antécédent.
• She tried to help the student whose lunch money had been stolen.
Elle a essayé d'aider l'étudiant à qui l'argent du déjeuner avait été volé.
Whose modifies lunch money and introduces the relative clause whose lunch money had been stolen, which describes the antecedent the student.

Substituting relative pronouns (Substituer les pronoms relatifs )
Most relative pronouns are capable of multiple functions and usages, meaning they can be used in place of one another in certain circumstances.
La plupart des pronoms relatifs ont des usages multiples, ce qui signifie qu'ils peuvent être utilisés les uns à la place autres dans certaines circonstances.
The table below gives a quick breakdown of when it is acceptable to use each relative pronoun:
Le tableau ci-dessous donne un aperçu rapide du moment où il est acceptable d'utiliser chaque pronom relatif: