Present Perfect Tense.

Peresnt perfect tense are used to explain the activity or a task that cannot be happen in not a specific time.sothey canot explain the exact happening of a task or a activity.It can explain the happening of a task  before the time in which that task can happen. For example;-

1. I have never seen him before.

Body of a tense;-

Positive tense;-
sub+has/have+verb 3rd form +obj.
Negative tense;-
sub + has /have+not +verb 3rd form +obj.
Interrogative tense;-
Has/have +sub +verb3rd form + obj+ ?