The past perfect is formed by using the helping (auxiliary) verb of “have” or “had” and the past participle form of the main verb, ending in “ed” or “en” for regular verbs. Irregular verbs have endings that vary. This tense is used to show a past event that preceded another event that is also in the past. Consider the following examples:
Example 1: She had arrived too late to watch the movie previews (she arrived late, and the previews were over already).
Example 2: The friends have attended the event every year since its first year (the friends attended the event, and they attended it every year since it began).