You can use .htaccess to show your visitors a custom made error page, instead of a standard server returned error code. The most common errors to create pages for, are Page Not Found (404) and Forbidden – Access Denied (403).
Add the following code to your .htaccess file:
ErrorDocument 403 http://one-example.com/forbidden.html ErrorDocument 404 http://one-example.com/notfound.html
Replace http://one-example.com/forbidden.html and http://one-example.com/notfound.html with the location of your custom made error pages.