Whenever you add a domain name as hosted in some account, you typically set a pair of Name Servers to point it to that particular provider. On their end, three records are set up automatically as soon as the domain name is added - one A record and two MX records. The former is a numeric address, or IP address, which “tells” the domain address where its website is, while the other two are alphanumeric and they indicate the server that deals with the emails for that particular domain address. The website and the e-mail hosting are often considered to be one thing, while they're in fact two different services. Having different records for them will allow you to have them with different companies if you would like. As an illustration, some new company might have outstanding uptime for your website, but you may not want to switch your e-mails from your current host and by using an A record to point the domain address to the former and MX records to have the e-mails with the second, you could get the best of both providers. These records are checked when you want to open a site or send an e-mail - in either case, the company 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'll see the needed site or your e-mail will be delivered.