Present perfect vs Past

Present Perfect vs. Past Simple
Usages
Is the time Sheila joined the Sierra Club the same or different?
Sheila has joined the Sierra Club.
Sheila joined the Sierra Club.

The use of the present perfect has more to do with our present perspective on the event rather than on the actual time at which it took place.
Present Perfect or Simple Past?
The simple past tense occurs with specific past-time adverbials. The core meaning of the past tense is remoteness. The use of specific past-time adverbials (e.g., yesterday, last year, 1990) makes the past tense obligatory. The use of certain more general temporal adverbials is commonly associated with the perfect (e.g., already, since, yet).
Present Perfect or Simple Past
Organise the phrases in the next slide into three columns headed used with simple past, used with present perfect and used with either.
Used with Simple Past
In the last century
during Kennedy’s lifetime
Three months ago
Throughout the 17th century
Used with Present Perfect
Up to now
Over the last hundred years or so
Since three months ago
This is the first time I
Lately
Since the Vietnam War
Within the last three months
Used with either
For three months
Recently
Today
After the Second World War
Present Perfect or Simple Past?
Even if a past-time adverbial isn’t explicit, the remoteness may be defined elsewhere in the context or simply implied:

John Lennon was a creative genius.
Present Perfect or Simple Past?
The past tense is used for a completed historical period versus an incomplete one:

My father lived here all his life.
My father has lived here all his life.
Present Perfect or Simple Past?
The function of the present perfect is to change the nature of the relationship between the subject and predicate – it emphasizes the predicated event’s result.

I’ve been to Japan twice already, but I still don’t speak much Japanese.
Overview
Past simple is used by speakers to talk about past events which are, or which they regard as, finalised, or over and done with.

Present perfect is used by speakers to talk about events which are still current, or which they want to highlight as being incomplete or still relevant.