Each registered domain has a minimum of two Name Server records that show where it is hosted i.e. by using these records you direct your domain to the servers of a particular hosting provider. That way, you've got both your website and your e-mails handled by the exact same provider. On the lower level of the Domain Name System (DNS), on the other hand, there is a variety of other records, for instance A and MX. The first one reveals which server handles the site for a given domain and is always an IP address (126.96.36.199), while the latter reveals which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, whenever you type a domain in your web browser, your request is forwarded through the global DNS system to the provider whose NS records the domain uses and from there you may be directed to the servers of a different provider provided you have set an IP address of the latter as an A record for your domain. Having different records for the website and the e-mails means you can have your website and your e-mails with two different companies if you wish.