You can use WP_Query for that :
$contentTypes = explode(',', $_POST['contents']);
$qry = new WP_Query( array(
'post_type' => $contentTypes
));
if( $qry->have_posts() ){
while( $qry->have_posts() ) {
$qry->the_post()
// Your code
}
}
Here is the [docs] ( https://codex.wordpress.org/Class_Reference/WP_Query ) for WP_Query