Why WWW vs non-WWW matters
Technically, example.com and www.example.com are different hostnames, and if both serve the same content without one redirecting to the other, search engines can treat them as duplicate content. This tool checks both versions of a domain, follows any redirects, and reports whether they correctly converge on a single canonical version.
Reading the two results side by side
Each version's final destination URL is shown after following any redirects, plus the HTTP status code returned along the way - comparing the two final URLs is how you confirm whether both versions actually converge on the same canonical page, or whether they're serving as two separate, competing versions of your site.
What a good result looks like
Both the bare and www versions being reachable and ending at the identical final URL is the healthy configuration - it means one version is correctly redirecting to the other (or a canonical tag is otherwise resolving the ambiguity), so search engines see a single, consistent version of your site rather than two competing ones.
What to do if they diverge
If both versions are reachable but end up at different final URLs, that's a sign your server configuration needs a redirect rule added - typically a 301 redirect from whichever version you don't want indexed to the one you do, configured at the web server or DNS/CDN level depending on your hosting setup.