past/present perfect分別20點

present perfect係以前做嘅事，用have，i/we/you/they have + pp，he/she/it has + pp，講緊現在嘅結果，i.e i have lost my pocket，i have no money now，我而家係冇錢。

past perfect係以前做過嘅事，用had + pp，i.e. i had lost my pocket yesterday，有時間性，但唔代表而家嘅事，昨日唔見銀包，但冇講而家有冇錢。

老師可能會教
perfect tense叫完成式吧
為了簡單地告訴你問題那兩個TENSE的分別，那麼我試把

present perfect tense叫剛完成式(唔係現在完成式)，意思是表達我現在寫/講這句之前一陣(通常由上一秒至一天之內)剛做了或剛開始做的...

past perfect tense叫已經完成式(唔係過去完成式)，意思是表達件事/行動是在過去開始亦已經在我現在寫/講這句時已經全部完成了...[已經有個了斷的才用這時式]

------Past and Present Perfect tense,priority given to simple and clear:-------
present perfect tense:-
I've lost my pen; I am unable to do my Homework.
I've lost my purse;+ I've no money now.
The present perfect Tense,though it indicates an action that took place in the past, is associated with the present idea of NOW,eg:-
I've never met your sister, (Up to NOW.)
I 've studied all the books. (So NOW I am fully informed.)
We've bought our monthly stock of rice. (So NOW our kitchen cellar is full.)
For an action just concluded when the resulting state is still present, eg:-This clock was working all right a moment ago but NOW it has stopped.
He has unlocked the door;there is something to let thief in.
I have lost my purse.+I've no money now.
I have lost my pen; I am unable to do my homework.

past perfect tense:-
I had lost my pen and I was unable to do Homework.
I had lost my purse and I was unable to pay!
"had+ a past pasticiple" is used to speak of an action concluded before a certain time in the past or before the time of the occurrence of another action(denoted by the Simple Past Tense) and yet continuing into it, eg,
TVB Lucita had learned English before she came to England.
When we got to the film the film had already started.
I didn't go to the exam because I had already failed,lost confidence.
He had unlocked the door, before you rushed out!
By the time I got the Doctor degree I had studied that class for 8 years!
I had lost my pen and I was unable to do my homework.
I had lost my pocket and I was unable to pay anything!
Some of the conjunctions with which the Past Perfect tense is often associated are:- before, when, after, once, as soon as, until.

http://www.ego4u.com/en/cram-up/grammar/simpas-preper

and

http://www.perfect-english-grammar.com/present-perfect-or-past-simple.html

these links should help! :)