You can create custom error pages and redirect to these pages by adding the below given codes in the htaccess pages

ErrorDocument 404 /404.php
ErrorDocument 500 /500.php
ErrorDocument 401 /401.php
ErrorDocument 403 /403.php

If index file is not there in a directory, visitors can view all the files in that directory.
You can prevent this by adding a single line code (Given Below)in your .htaccess file .

Options All -Indexes