Template Zara
Plugin version 2.2.8
The key set

1. I am adding code
<?php if(function_exists('radius_map_items')) { radius_map_items(); } ?>
to the home, and it does not work.

You are missing some javascripts.
Do not place anything to homepage, download latest version and use Zara Configurator plugin to setup map.

Download the latest version of Radius Search plugin or theme zara?

Tell me where is Zara configurator.

Thank you