Jolojo handles both 404 (page not found) and 403 (fobidden - which means page found but refused to deliver content) errors out of the box.
Error pages 404 and 403
The default pages just show a very basic message - 404 Not found and 403 Forbidden.
If you want to show nicer error pages to your users you need to create new pages and use the exact URLs below:
404 - /error/404
403 - /error/403
You can then add your own content to these pages.