Do you know what happens when you type google.com in your website? The web browser uses the domain name system to find the server that have your website. Here is where the nameservers are needed. They give the IP address (unique number that every computer connected to the internet must have in order to communicate with each other connected device) of the web server where the browser connects and ask for the website. The server gives back the html code back to the browser where it is rendered and displayed. There is much more processes happening underneath. You need the above two servers (primary and secondary) you need to add them at your domain registrar in order your site to work. After you update the nameservers at your dns registrar clear the dns cache (google for solution) and wait a few hours in order the changes to propagate.