Active and passive forms
The category of the voice indicates how the subject takes part in the action. There are three types of voices:
The active voice
When the verb is in the active voice, the subject is the motor of the action. It is the real agent of this action.
Le chat mange la souris. (The cat eats the mouse.)
The passive voice
On the contrary, to the passive voice, the subject becomes a spectator of the action and undergoes it.
La souris est mangée par le chat. (The mouse is eaten by the cat.)
Grammatically, the object complement moves to the left of the verb and becomes the subject while the subject becomes the agent complement on the right.
Not all verbs can be passive. Only verbs that are direct transitive can put themselves to the passive voice. A simple way to remember which verbs can be used for the passive voice is to see if there is a preposition after the verb as à, de, au, du etc. At this point, it is not possible to put the verb to the passive voice.
Moreover, not all status verbs can be put to the passive voice. Verbs which do not express an action but which attribute a characteristic (quality or defect) to a being or an object: être, devenir, sembler, paraître, rester...
The pronoun voice
The pronoun voice is formed with the personal reflective pronoun "se". In French, the two privileged modes are the active voice and the passive voice. Some grammarians classify the pronoun voice in the passive voice with an agent complement "se".
Il se promène dans son jardin. (He walks in the garden.)
Some verbs are conjugated only to the pronoun form. We speak then essentially pronominal verbs: se méfier, se désister, se souvenir, s'évanouir...
We speak of a reflexive pronoun voice when the subject and the pronoun are the same person. In the opposite case, we speak of reciprocal pronominal voice.
il s'est regardé dans la glace. (he looked at himself in the mirror - reflexive)
Pierre et Paul se sont regardés dans la glace. (Pierre and Paul looked at each other in the mirror - reciprocal)