When you add a domain name as hosted in some account, you usually set a pair of Name Servers to direct it to that particular provider. On their end, three records are set up automatically when the domain 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 reveal the server that deals with the emails for that specific domain address. The website and the e-mail hosting are usually regarded as one thing, while they're actually two different services. Having independent records for them will enable you to have them with different providers if you'd like. As an example, some new provider might have outstanding 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 could get the best of both companies. These records are checked when you want to open a site or send an email - either way, the provider whose name servers are used for the domain name 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.