Each and every domain name that is registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be created manually if required. For instance, the A record of a domain address is its IP address i.e. this record reveals where the web site is located; the MX records show where the emails are stored, while through an SRV record you can use a domain name for unconventional purposes, like 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 example, your current host provides good web hosting, but has troubles with the e-mail service, or you simply prefer to get a certain service from a specific company. While you will be able to set up and edit these records freely and without any restrictions as you own a given domain, some companies charge extra to give you this option.