Step by step instructions for custom 404 page.
Create and upload the page you want errors to take your visitors to (e.g. error.shtml or index.shtml etc. index.html (or index.shtml which has SSI capability) are the pages a browser usually goes to when no file is specified e.g. http://yourdomain.com)
Go to your control panel (yourdomain.com/cpanel - login if necessary.)
Click FILE MANAGER under Files Section.
Choose WEB ROOT (public_html/www)
Check box SHOW HIDDEN FILES (dotfiles).
Paste in the following:
ErrorDocument 400 /index.shtml
ErrorDocument 401 /index.shtml
ErrorDocument 403 /index.shtml
ErrorDocument 404 /index.shtml
ErrorDocument 500 /index.shtml
(Change index.shtml with the name of the page(s) you want visitors to go to when getting an error).
Click SAVE CHANGES
Now test it by entering yourdomain.com/blahblah.shtml