Each and every domain name that's registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be created by hand if needed. As an illustration, the A record of a domain is its IP address i.e. this record shows where the site is situated; the MX records show where the e-mails are stored, while with an SRV record you can use a domain for unconventional purposes, for instance a Voice-over-IP service. Being able to create and modify certain records enables you to have different services with different providers if, for example, your present host provides good web hosting, but has problems with the email service, or you simply prefer to get a certain service from a specific company. Even though you should be able to set up and edit these records freely and without any limitations as you own a given domain name, lots of companies charge extra to give you this option.