A 404 page represents a server code indicating that the page requested by a browser visiting a particular page URL could not be found. This message is provided by default on websites, but as a site owner, you can customize the 404 page to provide far more practical information to assist your visitors to locate the information they were hoping to find.
Design Shack has an excellent article, "What Makes a Great 404 Error Page?", that helps outline the kind of information and page structure you should consider incorporating to create a successful 404 page for your site.
Add a custom 404 page to your site
- Create a new Basic Page and provide it with the Title '404' and create the content you feel appropriate to help misdirected users locate the information they might need.
- Save your page.
- A site manager is required for the next step. Navigate to Manage » Configuration » System section » Basic Site Settings.
- Scroll to the bottom of the page to locate the "Default 404 (not found) page" field. Enter in your page's pathway. Example: /404
- Click the Save configuration button to finish.