How to create Custom Error Pages in Drupal

Drupal allows you to create custom Error 404 and Error 403 page. Follow below steps:

1. Create a basic type page with some content.
2. Navigate to:
   Home >> Administration >> Configuration >> System >> Site information
3. Set this new page as error 404 page as shown in below image.
   

This page will now act as Error 404 page. Similarly you can create Error 403 page.