C1: Verbs: Perfect Tense: Use the auxiliary verb “to have” + a past participle to form perfect verb tenses correctly. See Writing for Success Section 5.5 pp. 196-200 or the following: http://www.cws.illinois.edu/workshop/writers/perfectforms
Perfect tense shows action completed by a certain time in the past, present, or future:
I had eaten six marshmallows on the previous camping trip.
Roberta had listened to a lot of heavy metal in high school.
You have watched enough YouTube for one night.
He has stolen my t-shirts for the past year.
Future Perfect uses the helping verb “will” as well:
They will have visited Glamis ten times by the end of decade.
We will have known the Johnsons for a year when Thanksgiving comes.