如何在不访问该页面的情况下每分钟自动运行php脚本？

I'm developing website that will send email back to user automatically when they registered to my website. I have searched from internet, most of them said that i have to used cron jobs; the big problem foo me now is about cron jobs. I don't how to write it and also how to execute it. Can anyone gives me some example about it?I'm developing website that will send email bac