How do I form the passé composé and when do I use it?

The passé composé is a past tense in french, and is used for completed actions in the past. It has two equivalents in english: both "I ate" and "I have eaten". Therefore, if you are describing something which happened in the past, which is no longer going on, this is the tense you will have to use. It is formed using an auxiliary + the past participle of the verb. The auxiliary is either the present tense of the verb AVOIR or the present tense of the verb ETRE. ETRE is used for all reflexive verbs, and also for the verbs Monter, Rentrer, Sortir, Venir, Arriver, Naître, Descendre, Entrer, Retourner, Tomber, Rester, Aller, Mourir, Partir (MRS VANDERTRAMP). The past participle of the verb is formed differently depending on the ending. For ER verbs, you take off the ER, and add é. MANGER --> mangé For IR verbs, you take off the R. SORTIR --> sorti For RE verbs, you take off the RE and add u. DESCENDRE --> descendu (There are some irregular past participles which you also must learn) So, for an avoir verb, we might say: J'ai mangé - I have eaten / I ate And for an etre verb, we might say: Je suis allé - I have gone / I went