Each and every domain that is registered and hosted has a lot of DNS records - some of them are set up automatically when you host a domain, others can be set up manually if required. As an example, the A record of a domain address is its IP address i.e. this record shows where the website is located; the MX records reveal where the emails are stored, while using an SRV record you can use a domain address for unconventional purposes, for instance a Voice-over-IP service. Being able to create and modify certain records allows you to have different services with different providers if, for illustration, your current host provides dependable web hosting, but has troubles with the email service, or you simply prefer to get a specific service from a specific company. Though you can set up and edit these records freely and with no limits as you own a given domain, lots of companies charge extra to give you this option.