PRESENT PERFECT TENSE
They are formed using "has", "have" and another verb in the past participle form.
Examples are: has done / have taken / have spoken etc.
Tenses are used to attach the dimension of time to an action.
Present Perfect Tense is used to describe an action that happened in the past, and the effect of that action is still present. Example: I have taken my breakfast (He has bought the tickets. The purchase took place earlier but the tickets are still in my possession now. The fact that he has bought still stays.)
PAST PERFECT TENSE
Past Perfect tense can be used to indicate an even earlier action in the past.
For example, you are having dinner (7pm). You told your friend, "I had finished my work before I took a cab home." You completed your work EARLIER in the past (4pm). Then you took a cab home (5pm).
I hope this helps.