How to implement iflychat_check_access_filter?

I got these from the documentation:

You can display chat to a limited set of users in WordPress with the help of our filter named iflychat_check_access_filter.

Here is sample code to do this:

function my_custom_filter($access) {
$access = true;

/** Get current user information **/

global $current_user;
get_currentuserinfo();

/** Return $access as true or false based on your custom code */

return $access;
}
add_filter(‘iflychat_check_access_filter’, ‘my_custom_filter’);
But I cannot understand how to implement it. could you please show me more complete example?

https://wordpress.org/plugins/iflychat/