They don’t offer hosting but they do offer acceleration and security services (including a free tier that gets you a free CDN and DNS). You need to make them authoratative for your domain so as long as that works with your hosting provider you can try them.
Their acceleration service is a reverse-proxy that sits in front of your hosting which is why the whois records point to them. The real server for the other guy’s page is on a regular host somewhere behind the cloudflare servers.
Please do let me know if you have any questions about CloudFlare. Just a quick note that you do not need to change nameservers to point to us if you can activate through a CloudFlare hosting partner.
“Domain nameservers are always the web hosting names, I guess.”
Not really. You could easily have a registrar’s nameservers in there (GoDaddy) and have a different hosting provider than GoDaddy.
Some tips if you do signup for CloudFlare directly (helps prevent a lot of common issues/areas of confusion).
The good news is that we start at free:) Upgrading to a paid plan is entirely optional & based on features that you may want to utilize, but our basic services, including CDN, are free.
There’s no way to really test without signing up for the service (all sites are different) as to the site improvement you will see. Most sites, however, see about a 50% improvement in performance or so.