How to configure a 404 not found template
A 404 template can be configured in the settings of the web server. For instance in the Apache web server by means of the "ErrorDocument 404" setting.
The 404 template is typically a white page with black letters and a technical error message. It's recommended to design the 404 template in the same style as the website, so visitors who inadvertently land on the page aren't met by a boring technical page, but rather an inviting page that maintains the look & feel. In some cases, a practical solution could be to place a form on the 404 template, allowing the visitor to explain which link was used to get there and the webmaster to follow up on these incidents efficiently.