Sebas has explained how we use these tenses perfectly. BUT just notice that in Spanish we have 2 "pretéritos perfectos": "pretérito perfecto simple" (yo comí, yo estudié...) and "pretérito perfecto compuesto" (yo he comido, yo he estudiado). The relation between the English and the Spanish tenses is: Pretérito perfecto simple (yo comí) --> Past simple (I ate) Pretérito perfecto compuesto (yo he comido) --> Present perfect ( I have eaten) Pretérito pluscuamperfecto (yo había comido) --> Past perfect (I had eaten) Hope this helps!

Very good. The preterito perfecto is used with actions thah have ended alredy. "Yo comí" (I ate) means you have finished to eat. You use it when talking about actions that you did, and you've finished when you're talking about them. The pretérito pluscuamperfecto is used with actions that you did in the past, but that you did before another action. For example: "Yo ya había comido mi desayuno cuando llegó" means that you had eaten when he arrived, so, the action "eat your breakfast" is before the action "he arrived" I hope you understand.