The Passé Composé is a French verb tense used to express actions that have been completed in the past. It is formed using an auxiliary verb, either avoir or être, followed by the past participle of the main verb. For example, "J'ai mangé" means "I ate," where "ai" is the auxiliary verb and "mangé" is the past participle of manger. This tense is commonly used in spoken French and narrative writing to describe specific events or actions. The choice of auxiliary verb depends on the main verb; most verbs use avoir, while certain verbs, often indicating movement or change, use être.