When you add a domain name as hosted in some account, you normally set a pair of Name Servers to direct it to that particular provider. On their end, 3 records are set up automatically the moment the Internet domain 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 site is, while the other two are alphanumeric and they reveal the server that handles the emails for that specific domain address. The site and the email hosting are generally regarded as one thing, while they are actually two different services. Having separate records for them will allow you to have them with different providers if you want. For instance, some new provider could have superb uptime for your site, but you might 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 e-mails with the latter, you will get the best of both companies. These records are checked when you want to open a website or send an e-mail - in any case, the service provider whose name servers are used for the Internet domain will be contacted to retrieve the A and MX records and if you have set records different from their own, the correct web/mail server will then be contacted and you are going to see the needed site or your e-mail will be delivered.