Any time you add a domain as hosted in some account, you usually set a pair of Name Servers to point it to that specific service provider. On their end, three records are created automatically right after the domain is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the Internet domain where its website is, while the other two are alphanumeric and they show the server that deals with the emails for that particular domain address. The website and the email hosting are usually regarded as one thing, when they're in fact two different services. Having different records for them will allow you to have them with different providers if you would like. For instance, some new service provider can have outstanding uptime for your site, but you may not want to switch your e-mail messages from your current host and by using an A record to point the domain name to the first and MX records to have the emails with the latter, you can get the best of both companies. These records are checked whenever you want to open a site or send an email - either way, the provider whose name servers are used for the Internet domain is going to 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 are going to see the needed website or your email will be delivered.