How to embed a checkbox - newbie

I want to use a single checkbox field, from the doc:

    label: Header
    type: checkbox
    text: Do you want to display the header image?

My questions: how do I define it in the content/project file, what should I enter in the template ? does it automatically appear in the panel page? blueprint?
Thanks for your Help

The code you posted belongs in a blueprint. Blueprints tell the Panel which kind of fields to display. If you go to a project page in the Panel, you should see your newly added checkbox field there.

If you change and save the value in the Panel, it gets stored in the content file. You can also change it manually in there, you don’t need the Panel or blueprints for that.

The third step is the template. You can use code like this to check for the value:

<?php if($page->header()->bool()): ?>
  The header image should be displayed here.
<?php endif ?>

Of course you can exchange the text in the middle with any kind of HTML code you need.

PS: Please use Markdown code blocks when posting code in the forum. They use three backticks at the start and end on separate lines. I have changed it for you above, you can click the little pencil icon to see how it works.