You should first run the installer for WordPress which will generate a wp-config.php in your var>www>html>yrc>wp.
You can do it manually as well by copying the wp-config-sample.php to wp-config.php, do it only if you have understanding of what this file should contain.
To run the installer in your local host simply use the URL http://localhost/yrs/wp, this should initiate the installer.
Once this is done you can find a wp-config.php file in var>www>html>yrc>wp where you should add define('WP_ALLOW_MULTISITE', true);