Cacher is the code snippet organizer for pro developers

<?php

function schedule_name_cron_schedule($schedules){
    if(!isset($schedules['schedule_name'])){
        $schedules['schedule_name'] = array(
            'interval' => 60*60*24*3, // interval in seconds
            'display' => 'interval name'); // display text for example "Every three days"
    }
    return $schedules;
}
add_filter('cron_schedules','schedule_name_cron_schedule');

if(!wp_next_scheduled( 'schedule_function_name' )) {
  // if function doesn't exist for certain schedule, create it
  wp_schedule_event( time(), 'schedule_name', 'schedule_function_name' );
}

add_action( 'schedule_function_name', 'function_name_which_describes_what_the_cron_does' );

function function_name_which_describes_what_the_cron_does() {
  // do something cool here, for example send an email
  wp_mail('recipient', 'subject', 'content');
}