authoritative nameservers -Cloudflare

I changed the nameservers on my website intimatehair.com as instructed by Cloudflare. However, it did not make the site secure. I contacted them and received this comment: "You must point your authoritative nameservers to Cloudflare, this will delegate your DNS configuration to Cloudflare. It is not sufficient to simply set NS DNS records for Cloudflare; you must set your authoritative nameservers with your domain registrar." Okay, way above my pay grade. How do I do that? Thanks!