perfect tense

Present Perfect Tense is used for describing a past action’s effect on the present: He has arrived. Now he is here. This holds true for events that have just been secluded as well as for events that have not yet occurred.
The pattern :
(+) S + has/have + V3 + O.
(-) S + has/have + not + V3 + O.
(?) Has/Have + S + V3 + O + ?
Present perfect is formed by combining have/has with the main verb’s past participle form:
— I have arrived.
A negation is produced by inserting not after have/has:
— I have not arrived.
Questions in present perfect are formulated by starting a sentence with have/has:
— Has she arrived?
Past Perfect Tense is a kind of tense that is used to describe an action or an event that started in a certain time in the past and completed or finished till certain time in the past too; or past perfect tense is used to express an action or an event that had happened before the other event or action happened
The pattern :
(+) Subject + had+verb III+cmplement
(-) Subject + had not+ver III+complement
(?) Had + subject +verb III+complement
Adverbs used :
from 1998 to 1999, once, twice, etc.