Translation:My parents cooked for my friends.
In French the Passé Composé: avoir/être (present) + main verb (past participe) corresponds to the meaning of (simple) past in English and other languages. To express 'had cooked' we have to use the Plus-que-Parfait, avoir/être (imparfait) + main verb (past participe) , which would be: "Mes parents avaient cuisiné pour mes ami(e)s." To grasp the difference, here is a sentence with both tenses: "Ma grand-mère était sortie de l'hôpital le jour où mes parents avaient cuisiné pour mes amis."
The difference between "has cooked" and "had cooked" is confusing to some. The "has cooked" comes from Passé composé "ils ont cuisiné" (also "cooked"), and the "had cooked" comes from the Pluperfect tense "ils avaient cuisiné". The Pluperfect tense is used to refer to an action in the past which occurred before another action in the past (usually expressed in Passé composé or Imperfect). Two examples:
- J'avais étudié la leçon que le professeur a expliquée = I had studied the lesson which the teacher explained. First I studied the lesson; then the teacher explained it. Both actions are in the past. The action that occurred in the past before the other past action is in the Pluperfect.
- J'ai étudié la leçon que le professeur avait expliquée = I studied the less which the teacher had explained. In other words, the teacher explained the lesson first and then I studied it.