Whenever you add a domain name as hosted in some account, you normally set a pair of Name Servers to point it to that particular service provider. On their end, 3 records are created automatically right after the Internet domain is added - one A record and two MX records. The first one is a numeric address, or IP address, that “tells” the domain where its website is, while the other two are alphanumeric and they show the server that deals with the emails for that specific Internet domain. The website and the e-mail hosting are typically considered to be one thing, while they're actually two different services. Having separate records for them will permit you to have them with different providers if you would like. For instance, some new provider can have excellent uptime for your website, but you might not want to switch your e-mails from your current host and by using an A record to point the domain to the former and MX records to have the emails with the second, you could get the best of both providers. These records are checked whenever you want to open a site or send an email - in either case, the provider whose name servers are used for the Internet domain will be contacted to retrieve the A and MX records and if you have set records different from their own, the correct web/mail server will then be contacted and you'll see the needed website or your e-mail is going to be delivered.