posts_per_page= is used to limit the number of posts that are retrieved by query_posts() wordpress loop

Example :

query_posts ( 'cat=3&posts_per_page=6' ); // posts_per_page

if (have_posts ()):

	while (have_posts()):
	
		the_post ();
		the_title (); // printing title of post
		
		echo "On " . the_time ( 'F jS, Y' ); // printing time of post
		 
	endwhile;
	
 endif;