You can customize error pages, but for that you need to know the error number like 404 for page not found.

Now in .htaccess file you need to enter:

ErrorDocument errornumber /file.html

For example if, there is a file, NotFound.htm in error directory, and you wanted to use it for the 404 error, then you need to enter:

ErrorDocument 404 /error/NotFound.htm

These are some of the most common errors:

401 – Authorization Required
400 – Bad request
403 – Forbidden
500 – Internal Server Error
404 – Wrong page