Problems with perfect tenses

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I have some problems with Present Perfect tenses. The thing is that if I want to talk with my friends or if I want to write an email, then what should I focus on ?

For example :

I have a plenty of time ----------- I have got a plenty of time.

Of course we can add "now or tommorow to indicate which time to use, but what if there aren't any additional times that indicate which one to use ?

Next example:

This city has been occupied so be carefull ----------- This city was occupied so be carefull.

New gadget has been annouced ----------------- New gadget was annouced

I don't know how should I know which one to use (if there is no time emphesised) when I want to write an Email or talk with somebody. Somebody can say that Present Perfect is about past action but we see the result right now, but I often see that people describe the past action with past simple but they still see the result of that action. It's pretty the same when we talk about Present simple. I just don't get it.

Thanks for any answer and help.