Your question is a bit unclear.
Do you want wp_cron() to make things happen somewhere else?
Then you’d need to set up some kind of receiving URL on that something else that you could call from your site. And you’d need to create a function in your WordPress installation that would call that URL. Finally, you’d need to add a call to your function into your cron table.
Remember here that wp-cron() only will run when the website is called, for instance by any visitor requesting a page.
Or do you want wp_cron() to be initiated by some external service? It’s possible to exclude wp_cron() from the handling of every page visit and instead have a real cronjob on the server or some external cron-provider visit a specific URL to “kick” wp_cron(). This can be useful if your site receives a lot of visitors and you don’t want every visit to include a check for pending wp_cron() tasks. Search on the net for “disable wp_cron” and you’ll find lots of information.
