Any time you add a domain name as hosted in some account, you usually set a pair of Name Servers to direct it to that specific provider. On their end, 3 records are set up automatically when the domain address is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the domain name where its website is, while the other two are alphanumeric and they show the server that handles the e-mails for that specific domain name. The website and the e-mail hosting are generally considered to be one thing, while they are actually two different services. Having separate records for them will enable you to have them with different companies if you would like. For example, some new service provider can have exceptional uptime for your site, but you may not want to switch your e-mails from your current host and by using an A record to point the domain to the first and MX records to have the emails with the second, you can get the best of both companies. These records are checked when you want to open a site or send an e-mail - in any case, the provider whose name servers are used for the domain 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 is going to be delivered.