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 specific company. On their end, 3 records are created automatically when the domain name is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the domain name where its site is, while the other two are alphanumeric and they show the server that manages the emails for that particular domain address. The website and the email hosting are usually regarded as one thing, while they're in fact two different services. Having different records for them will allow you to have them with different providers if you'd like. As an example, some new service provider might have fantastic uptime for your site, but you might not want to switch your emails 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 could get the best of both providers. These records are checked when you wish to open a website or send an email - 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 right web/mail server will then be contacted and you'll see the needed site or your e-mail will be delivered.