Basically, when you want get posts, you should think about WP_Query
. It’s already in the docs for your question.
You can get posts by an author like this
$query = new WP_Query( array(
'author' => AUTHOR_ID,
'posts_per_page' => 5
) );
You can even get posts by more than one author, like this
$query = new WP_Query( array(
'author__in' => array( AUTHOR_ID, ANOTHER_AUTHOR_ID ),
'posts_per_page' => 5
) );
Because WP_Query is sort by date and order descending by default so you don’t need specify that information.