You can use the wp_insert_post to do this
//sample code
if(isset($_POST['submit_button'])){
$my_post = array(
'post_title' => $_POST['title'],
'post_date' => date("Y-m-d H:i:s"),
'post_content' => $_POST['description'],
'post_status' => 'pending',
'post_type' => 'post',
'post_author' => $user_id
);
$the_post_id = wp_insert_post( $my_post );
}
for more info about wp_insert_post visit this page http://codex.wordpress.org/Function_Reference/wp_insert_post