Here's how it works:
* "Se réveiller" is the verb "to wake up".
* "S'est" is the third-person singular of the reflexive pronoun "se" in the past tense.
* "Réveillé" is the past participle of the verb "se réveiller".
Here are some examples:
* Il s'est réveillé à 7 heures du matin. (He woke up at 7 am.)
* Elle s'est réveillée en sursaut. (She woke up with a start.)
* Le bébé s'est réveillé pendant la nuit. (The baby woke up during the night.)
Note: There are other ways to express waking up depending on the context. For example, you could use:
* "s'est levé" (literally "got up") which implies getting out of bed.
* "a ouvert les yeux" (literally "opened his/her eyes") to emphasize that someone became conscious.
Let me know if you have any other questions!