Every domain which is registered and hosted has quite a lot of DNS records - some of them are set up automatically when you host a domain, others can be created manually if needed. For example, the A record of a domain is its IP address i.e. this record shows where the website is located; the MX records reveal where the e-mails are managed, while with an SRV record you can use a domain address for unconventional purposes, like a Voice-over-IP service. To be able to set up and modify specific records enables you to have different services with different companies if, for example, your present host provides good web hosting, but has difficulties with the email service, or you simply prefer to get a certain service from a certain company. While you should be able to set up and edit these records freely and without any limitations as you own a given domain address, some companies charge extra to give you this option.