Any time you add a domain name as hosted in some account, you typically set a pair of Name Servers to direct it to that particular provider. On their end, three records are created automatically as soon as 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 site is, while the other two are alphanumeric and they indicate the server that deals with the e-mails for that specific Internet domain. The site and the e-mail hosting are typically perceived as one thing, when they're in fact two different services. Having separate records for them will permit you to have them with different providers if you wish. For instance, some new company might have superb 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 first and MX records to have the e-mails with the second, you can get the best of both companies. These records are checked when you want to open a website or send an e-mail - in either case, the provider whose name servers are used for the domain address will be contacted to retrieve the A and MX records and if you have set records different from their own, the right web/mail server will then be contacted and you'll see the needed site or your e-mail is going to be delivered.