Jaka jest różnica między tymi zdaniami: I wrote the letter. I have written the letter. I czy można tych czasów używać zamiennie w pewnych przypadkach?
There is a difference between the two tenses.
In some cases, you can use either.
In most cases, the simple past will do the job.
In some (there are few and far between) cases, the present perfect is is much better. You must know the difference.
When in doubt, use the simple past.