Report is not send automatic by email

I try to send automatic weekly a report by email. I ve done the settings in >Administration>emailreport. If I click on “send report now” I got it correct in my mailbox, but it is not send automatic on the requested time. I understand that I have to do something with cron, but this part is abracadabra for me. I send a test in my browser, I got a report in the mail, but complete empty. Can somebody tell me how to setup the cron?