Any time you add a domain name as hosted in some account, you normally set a pair of Name Servers to point it to that specific 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 Internet domain where its site is, while the other two are alphanumeric and they show the server that handles the emails for that particular domain. The website and the email hosting are typically regarded as one thing, while they are in fact two different services. Having independent records for them will enable you to have them with different providers if you wish. For instance, some new service provider might have exceptional uptime for your site, but you might not want to switch your emails from your current host and by employing an A record to point the domain name to the first and MX records to have the e-mails with the latter, you could get the best of both companies. These records are checked when you want to open a site or send an e-mail - either way, the provider whose name servers are used for the domain address is going to be contacted to retrieve the A and MX records and if you've set records different from their own, the correct web/mail server will then be contacted and you're going to see the needed website or your e-mail is going to be delivered.
