The past perfect tense refers to past time .
example :
Ali had played football before he went back home.
use the past perfect tense of the verb .
•to tell what you have done recently/ lately.
•to tell what you have just or already done.
•to tell what you have never/ ever done.
•to tell what you have done so far/ up to now.
•to tell what you have done today/ this week/ this month/ this year.
•It can describe either present or past activities
URL :
http://www.studyspanish.com/lessons/presperfect.htm
http://en.wikipedia.org/wiki/Present_perfect
http://www.englishclub.com/grammar/verb-tenses_present-perfect.htm
http://www.englishclub.com/grammar/verb-tenses_past-perfect_u.htm
http://www.past-simple.com/Present-Perfect.htm
http://en.wikipedia.org/wiki/Pluperfect