Every registered domain name has no less than 2 Name Server records that show where it is hosted i.e. by using these records you direct your domain address to the servers of a particular hosting provider. In this way, you've got both your website and your emails handled by the same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, for example A and MX. The former shows which server deals with the site for a given Internet domain and is always an IP address (188.8.131.52), while the second one indicates which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). As an example, when you type a domain address in your web browser, your request is forwarded through the global DNS system to the company whose NS records the domain address uses and from there you could be forwarded to the servers of a different company provided you have set an IP address of the latter as an A record for your domain. Having independent records for the website and the e-mails means you may have your website and your e-mails with 2 different companies if you'd like.