How to use cloudflare CDN

I have have an account in cloudflare,so I want to set dns Server but It doesn’t supported , so How can I use cdn with cname?

What do you mean by “dns server but it doesn’t supported”?

A very important first question: are you using a free subdomain or own domain name?

My own domain,I want to use My own namesever

What do you mean by “dns server but it doesn’t supported”?