A 404 page should include a link back to the home page or site map of your website so users can quickly get back to what they were searching for. A search box, if you have a site search, is also a good idea to add to a 404 page. Other than that, keep the page minimal, remove distractions and get the user off the 404 error page as quickly as they got on.
Keep in mind most users may not be so savvy when it comes to the use of a custom 404 page and other Internet jargon so simple explanations in English are key! Although, keeping it minimalist does not have to mean “boring” when it comes to the use of a custom 404 page.
Custom 404 page is simple and this site can explain in detail how to create depending on your server
By following these steps, even the most novice can achieve success in making a custom 404 page.
404s can appear if a URL is mistyped, a search engine link is out of date, or if a link on the site is broken.
When pages are deleted instead of redirected with a 301, they turn into 404s Not Found Pages.
If you have old pages on your website that you want to remove or rename, use a 301 redirect to preserve search engine rankings and pass on backlinks and/or page rank. You can even redirect whole websites to new ones through the use of 301 redirects. The use of 301 redirects is easy to do and is very search engine friendly.
Follow this guide to learn how to implement many different types of 301 redirects.
The term "301" stands for "moved permanently".
301 redirects are created by using a .htaccess file