We can use Past Simple with specified finished (period of) time and the verb denoting a complete action. We never use Present Perfect in this case.
last year, last month,
one millisecond ago,
a hundred years ago,
on the 11th of August,
from 1998 to 2003,
at 5 in the morning, from 2 to 5, between 4 and 7 pm, etc
We went to the movies at 4
We can use both Present Perfect and Past Simple with unspecified (period of) time.
in the last few days,
before, in the past,
many / several / a few times,
x times, never, ever, always,
in my whole life
(all of these belong to an unspecified period in the past, usually referred to as the entire past until now)
this is the first time (in my entire past until now)
We normally use Present Perfect here:
I have done it before
When we talk about past events or narrating a story, or when the time is implicitly complete, we can use Past Simple:
He never went to the movies. He was a kind of a silent, shy young man who spent all his free time at home
If we want to put an accent on the process, and we don’t want to stress on the fact of performing an action, we can use Past Simple:
I did it before, but I don’t remember how (my plan: discuss it with native speakers)
You definitely need to revise the lesson on Present Perfect: The exact moment in the past is not specified to understand this lesson better.