Perfect Tenses

The present perfect tense is a perfect tense used to express action that has been completed with respect to the present. (The word perfect in its name refers to the idea of completion—of being now finished—rather than to perfection in the sense of "no flaws".) "I have finished" is an example of the present perfect. The present perfect is a compound tense in English (and in many other languages), meaning that it is formed by combining an auxiliary verb with the main verb. For example, in modern English, it is formed by combining a present-tense form of the auxiliary verb "to have" with the past participle of the main verb. In the above example, "have" is the auxiliary verb, whereas the past participle "finished" is the main verb. The two verbs are sometimes labeled "V1" and "V2" in grammar instruction.

Present perfect is formed by combining have/has with the main verb’s past participle form :
- I have arrived
- I have not arrived
- 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 :
(+)S+had+VIII+complement
(-)S+had not+VIII+complement
(?)Had+S+VIII+complement

Example :
(+)We had eaten before they come
(-)We had not eaten before they come
(?)Had they eaten before we come ?

Adverbs used :From 1998 to 1999, once, twice, etc