How to create custom error pages?

We use Nginx as the web server. Its configuration regarding error pages is:

error_page 403 /custom_403.html;
error_page 404 /custom_404.html;
error_page 500 502 503 504 /custom_50x.html;

Therefore, you need to create the files

• custom_403.html
• custom_404.html
• custom_50x.html

in the main directory.