Any time you add a domain as hosted in some account, you typically set a pair of Name Servers to direct it to that particular service provider. On their end, three records are created automatically right after the domain address is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the domain where its website is, while the other two are alphanumeric and they reveal the server that manages the e-mails for that particular domain address. The website and the email hosting are often considered to be one thing, when they are in fact two different services. Having separate records for them will allow you to have them with different companies if you would like. For instance, some new 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 Internet domain to the former and MX records to have the emails with the latter, you will get the best of both providers. These records are checked when you wish to open a website or send an email - either way, the company whose name servers are used for the domain name will be contacted to retrieve the A and MX records and if you've set records different from their own, the right web/mail server will then be contacted and you will see the needed site or your e-mail will be delivered.