Just to append to @pixeline's answer (tried to add a simple comment but the site said I needed 50 reputation).
If you are writing your plugin for the admin section then you should use:
add_action('admin_enqueue_scripts', "add_my_css_and_my_js_files");
The admin_enqueueu_scripts is the correct hook for the admin section, use wp_enqueue_scripts for the front end.