Custom article field I can use and show on front-end?

So right now in the admin panel, I can put title and content for the post. How can I add one more input field and use it for additional content (let it be a special note from the author)?

You can extend the default yaml and add your field.

title: Special
'@extends':
    type: default
    context: blueprints://pages

form:
  fields:
    tabs:
      type: tabs
      active: 1
      fields:
        content:
          fields:
              header.specialnote:
                type: textarea
                label: Special note from the author

This should append your field to the 'content' tab

@paulmassendari thanks! What is the "default" yaml file you have in mind?

@justshipit the default Grav page is defined in https://github.com/getgrav/grav/blob/develop/system/blueprints/pages/default.yaml