This shows you broken links on your site - pages that no longer exist but are still being visited, either from old links elsewhere on the web or from search engines with outdated results.
Go to Dashboard > Marketing & SEO > SEO > 404 Broken Link Manager.
A 301 redirect tells search engines the page has permanently moved, passing along any SEO value the old page had built up, rather than losing a visitor to a dead end.
Broken links hurt both user experience and SEO. Regularly checking this report, especially after renaming or deleting pages, keeps your site clean in Google`s eyes.