How to make a 404 page
When a user sees your 404 page the browser should also see a 404 HTTP code. It is important to make sure that the code is 404 and not 200 as otherwise search engines are likely to think the 404 is a page that needs to be indexed.
Most Servers (like Apache)
90% of the web servers make use of a file called .htaccess (note the dot at the start of the file name). You are going to want to edit this file.
Open it up (or create it if it is not there) and add this line:
ErrorDocument 404 /404page.html
This assumes that the page you want to show users is called "404page.html" if it is called "notSoBrill.php" then you need to change the line to reflect this.
Other Servers (Like IIS)
Windows/ISS servers are not so simple and you would be better off contacting your hosting provider for details on how they have set this up for you.
If you have access to you web.config file then you might be able to make changes there if you know what you are doing.
404 is code for File Not Found - 404 pages are good for having fun with.
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