Whenever you add a domain name as hosted in some account, you usually set a pair of Name Servers to direct it to that particular service provider. On their end, three records are created 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 address where its website is, while the other two are alphanumeric and they show the server that handles the e-mails for that particular domain name. The site and the email hosting are often perceived as one thing, when they're in reality two different services. Having separate records for them will allow you to have them with different providers if you wish. As an illustration, 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 address to the first and MX records to have the emails with the latter, you could get the best of both providers. These records are checked when you want to open a website or send an email - 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've set records different from their own, the right web/mail server will then be contacted and you are going to see the needed site or your email will be delivered.