What is the 'passé composé' tense and when is it used?

This tense is one of the past tense used to describe completed actions.It can often be confused with the imperfect tense- however the passé composé is used when the action is not continued into the present and is not reoccurring; unlike the imperfect tense. For example I ate an apple is the passé composé whilst I was eating an apple is the imperfect because you may still be eating the apple now.Formation:There are two key parts to the formation: 1) the auxiliary verb which is formed from the present tense of either être or avoir- it will be être if it is a reflexive verb eg se doucher or if it is part of MRS VANDERTRAMP (montrer, rester, sortir, venir, arriver, naître, descendre, entrer, rentrer, tomber, retourner, aller, mourir, partir)Once you have decided on the auxiliary verb you can then conjugate the verb you want to use2) For ER verbs remove the ER ending and add an é/ for IR verbs remove the IR ending and add an I/ for RE verbs remove the RE ending and add a U3)Some of these verbs have an irregular past participle like naître which becomes né and faire which becomes fait4) If the verb that you are conjugating here takes être (because it is reflexive or in MRS VANDERTRAMP) then you MUST agree the verb- eg they went out= ils sont sortiS (the extra S is the agreement because ils is plural) You can then collate both parts together to form the passé composé5) EG I ate an apple- to eat = manger- it is not reflexive nor does it come under MRS VANDERTRAMP- therefore you use the avoir present tense not être- so it would be j'ai- then manger is an ER verb so remove the ER and add an é- so the whole verb becomes j'ai mangé une pomme