To form the past tense you need 2 parts: the verb avoir as your auxilliary or 'helping' verb formed in the present tense, and a past participle. Avoir is formed according to who is carrying out the action, e.g. I ate an apple, you would need the I or je form. The present tense forms of avoir are: j'ai, tu as, il/elle a, nous avons, vous avez, ils/elles ont, and these need to be learned as they do not follow a pattern. So far we have j'ai but we still need to say 'ate'. The past participle of regular verbs is formed by taking the infinitive, in this case to eat = manger, removing the -er = manger and adding an e with an accute accent: é so to say i ate an apple you would need the 'helping verb' according to the oerson, j'ai and a past participle, mangé. Therefore our sentence, I ate an apple, would be j'ai mangé une pomme.