Each and every domain name that's registered and hosted has quite a lot of DNS records - some of them are created automatically when you host a domain, others can be set up by hand if necessary. As an example, the A record of a domain name is its IP address i.e. this record reveals where the web site is located; the MX records reveal where the e-mails are stored, while through an SRV record you can use a domain name for unconventional purposes, including a Voice-over-IP service. To be able to set up and modify certain records enables you to have different services with different companies if, for instance, your current host provides good web hosting, but has issues with the email service, or you simply prefer to get a certain service from a certain company. Although you should be able to create and edit these records freely and with no limitations as you own a given domain name, many companies charge extra to give you this option.