Pablo, I face the same problem, too. The present perfect isn't existed in Arabic, but I'm trying to do my best to learn/use it. It's a bit tricky! But what about the "Imperfect", "Pluperfect", "Subjunctive" in Spanish? They aren't existed in English grammar, and Arabic either. :D

We use the Present Perfect to say that an action happened at an unspecified time before now. The exact time is not important. You CANNOT use the Present Perfect with specific time expressions such as: yesterday, one year ago, last week, when I was a child, when I lived in Japan, at that moment, that day, one day, etc. We CAN use the Present Perfect with unspecific expressions such as: ever, never, once, many times, several times, before, so far, already, yet, etc. Examples: I have seen that movie twenty times. I think I have met him once before. There have been many earthquakes in California. People have traveled to the Moon. People have not traveled to Mars. Have you read the book yet? Nobody has ever climbed that mountain. A: Has there ever been a war in the United States? B: Yes, there has been a war in the United States.

we used the simple past when we want to indicate an action made on the past. Often this verbal form is used with adverbs like YESTERDAY - LAST YEAR etc etc. Instead the Presente perfect is used to indicate an action that is happened in the past but that have some connection with the present still. Exemples are: I have just eaten, i have already drunk. Also in an italian language there are these verbal forms called PASSATO e PASSATO PROSSIMO. Of course someone will teach that I have just written better. Gaetano

Hello