Every domain name that's registered and hosted has lots of DNS records - some of them are created automatically when you host a domain, others can be set up manually if necessary. As an example, the A record of a domain is its IP address i.e. this record reveals where the web site is situated; the MX records reveal where the e-mails are handled, while through an SRV record you can use a domain for unconventional purposes, including a Voice-over-IP service. Being able to create and modify certain records enables you to have different services with different providers if, for instance, your present host provides good web hosting, but has difficulties with the email service, or you simply prefer to get a particular service from a particular company. While you will be able to set up and edit these records freely and without any limitations as you own a given domain address, a lot of companies charge extra to give you this option.