What it can do for a website
A site can use Cloudflare’s DNS to help browsers find it. If the site also routes visits through Cloudflare, Cloudflare acts as a reverse proxy: it handles requests before they reach the site’s server. Its CDN can serve nearby copies of content, and its web application firewall (WAF) can block unwanted requests.
When something goes wrong
A Cloudflare security rule might block a visit. A slow page may involve the site’s server or its connection; an old-looking page may be a cached copy. Knowing which service is involved helps narrow down the cause.