I purchased my domain name from Namespace and am hosting my application on Digital Ocean. In order to point my domain name to my digital ocean droplet all I had to do is enter the digital ocean nameservers on Namespace then I was able to set my domain name on digital ocean. How does digital ocean know that I own that domain name?
The answer is in your own question: you have access to the domain(/zone) nameservers configuration, so you're the owner (or at least you have some privileges over that domain)l