I hope I got it right.
The present perfect tense can be thought of as a tense designed to present us with some kind of a result or a state of affairs, mainly over a certain period of time.
I've never seen this guy before.
Here I'm letting the listener/reader know that this is the 1st time I see the guy.
Basically, in the long run, reading (and reading quality literature, like H.G. Wells or J. Grisham) can help you grasp the way these tenses really work.
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