In English grammar, both the past tense and the present perfect tense denote an action that has been completed, e.g., “He went to Agra.” (past), and “He has gone to Agra.” (present perfect). But the difference is this: in the first sentence, we do not know whether the result of the action still continues: whereas, in the second sentence, it is clear that the result of the action continues, viz., that he has not yet returned.

(a) He went to Agra. The action is completed: the result of the action may or may not continue.
(b) He saw the Tajmahal. The action is completed: the result of the action may or may not continue.
(c) He ate the cake. The action is completed: the result of the action may or may not continue.
(d) He has gone to Agra. The action has been completed: the result of the action continues, he has not yet returned.
(e) He has seen the Tajmahal. The action has been completed: The result of the action continues: The memory of the building still persists.
(f) He has eaten the cake. The action has been completed: The result of the action continues: Perhaps he now regrets his action or it may be he wants to eat the cake again.

N. B. -One thing, however, should be noted in connection with the use of the present perfect tense; if an adverb or adverbial phrase denoting a past period of time is definitely mentioned, the tense used must be the past and not the present perfect, no matter whether the result of the action continues or not.
He went to Agra yesterday, but has not yet returned.

Read more : The Tense

Read more : Solve Tense Exercise