What is the difference between using different tenses?

Hi there, first of all merry christmas

I want to know what is the difference between those two sentences :-

When I was playing, John wrote the letter.

When John was writing the letter, I played football.

 

Is there a difference in the meaning ? and thanks

thanks

|------------------------------------------------| I played
|------------------------| John wrote the letter.

When John was writing the letter, I played football.
|------------------------------------------------| John wrote the letter.
|------------------------| I played




i didn't get it.