Any time you add a domain name as hosted in some account, you usually set a pair of Name Servers to point it to that specific company. On their end, three records are set up automatically right after the domain name 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 site is, while the other two are alphanumeric and they reveal the server that manages the emails for that specific domain address. The website and the e-mail hosting are generally thought to be one thing, while they're in reality two different services. Having independent records for them will allow you to have them with different providers if you'd like. For instance, some new service provider can have excellent uptime for your website, but you may not want to switch your emails 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 providers. These records are checked when you wish to open a site or send an e-mail - in any case, the service 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 are going to see the needed website or your e-mail is going to be delivered.