Here’s how to set the nameservers if you have already bought the domain (shown here on GoDaddy, but the concept is the same and nameservers are the same on any registrar).
Want to see it again? This is an older video covering the same topic. If you did the above, you don’t need to see it, but if it helps, here’s the older version…
And if you’re buying a new domain, we recommend GoDaddy just because their service rocks – but ignore all the upsells. Skip right to the bottom, but before you check out, set the nameservers like this: