How does perfect tense work in French?

In French, to talk in the past about an event, a precise action (that didn't last), we use the perfect tense. It is basically formed using two components : an auxiliary verb and a past participle. There are two auxiliary verbs: "être" and "avoir" conjugated in the present tense. The use of these auxiliary verbs depends on the situation, and the same past participle with a different verb would have a totally different meaning. For instance, she has eaten would be "Elle a mangé" and she is eaten would be "Elle est mangée" - it is quite similar as in English in the end. Another really important point here is to notice that the past participle of the verb "manger" (to eat) doesn't always agree with the subject ; using "être", the past participle always agrees in gender and number with the subject (here "elle" is feminine, therefore we get "mangée”). On the contrary, using “avoir”, the past participle doesn’t always agree with the subject (here we had “mangé”, even with a feminine subject). Note: Under certain conditions, the past participle agrees with the subject even using “avoir”. Also we need to be able to form correctly the past participle for every verb, which can sometimes be formed using basic rules, but for some has to be learnt by heart.