Pronoun

Relative pronouns

qui	who, which: in the subject function it refers to people and things, after the preposition - only to people
que	which, whom : in the object function - both about people and things ; it is also a conjunction meaning in English that
quoi	about things after a preposition
dont	whose
où	for place and time description, most commonly: where
lequel	variation by genus, used in place of "qui" and "que" when there is probability of misunderstanding

Examples :
Qui :
Subject function (who, which – both persons and things) . We can see that a verb is after qui.
Je connais l'homme qui est ici.
Je mange une pomme qui est rouge.

After prepositions (only persons)
C'est l'homme avec qui il a parlé hier.
C'est la femme de qui tu m'as racconté.

Que :
Object function (whom, which – both persons and things, sometimes omitted in English). We can see that the subject is immediately after que:
Je vois un homme que je connais.
Je vois la voiture que je veux acheter.

Conjunction function (English that, often omitted in English):
Je sais qu'elle est belle.

Quoi :
After prepositions (only things)
C'est la chose avec quoi il joue.