Your domain name registrar will have default nameservers, and in most cases, those will be fine (unless you have a specific reason to use different ones.)
But what are nameservers?
You might think about nameservers as being like the contacts in your smart phone. You have an entry called “Mom,” and your phone has a contacts database that stores the actual phone number for dear old Mom. So when you click on Mom’s name a phone call gets placed to Mom’s phone number.
In that analogy, the DNS is like the entry of a specific phone number in the Contacts. But in this case, it is saying “when any browser is looking for xyz.com domain, send them to IP address 111.222.33.44, which is the web server that stores and serves the pages of my website.”
This might look a little scary to set up but there really isn’t much to it. When you have registered a domain, and you have the IP address of where your website will be hosted, you need to make a DNS entry that associates your domain name with that IP address.