What is the difference?
Both tenses talk about the past, but they are used in different situations. The key question is: does the time matter?
Present Perfect: have / has + past participle — the time is unknown or not important
Simple Past: past form of the verb — a specific time is mentioned or understood
Use the Present Perfect when...
...you talk about an experience without saying when it happened.
I have been to Japan. (at some point in my life — when is not important)
She has tried sushi. (we don't know or care when)
They have seen that film.
Use the Simple Past when...
...you mention a specific time or the situation is clearly finished and in the past.
I went to Japan last year. (specific time → simple past)
She tried sushi when she was in Tokyo. (specific situation)
They saw that film on Saturday.
Common Time Expressions
Present Perfect: ever, never, before, once, twice, three times, in my life
Simple Past: yesterday, last week, last year, in 2019, this morning, two days ago, when I was a child
⚠ Common mistakes:
✗ I have gone there last year. → ✓ I went there last year. (specific time = simple past)
✗ Have you ever ate Thai food? → ✓ Have you ever eaten Thai food? (have + past participle)
✗ She has called me yesterday. → ✓ She called me yesterday. (yesterday = simple past)