configuration of .htaccess for add_rewrite_rule to make sense

Question

I am trying this code from codex wordpress site

function custom_rewrite_basic() {
    add_rewrite_rule('^leaf/([0-9]+)/?', 'index.php?page_id=$matches[1]', 'top');
}
add_action('init', 'custom_rewrite_basic');

How must by .htaccess file must be configured for above code to make sense? If I put the basic wordpress .htaccess configuration file then I get redirected to same page.

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

Answer 1

after adding a new rule, you have to flush the rewrite-rules in order to use them

that can be done with the "flush_rewrite_rules" function http://codex.wordpress.org/Function_Reference/flush_rewrite_rules

or it can be done in going in the Administration Screens -> Settings -> Permalink and just saving without changing something on this screen