Accessing Collections in Twig

Hi,
I did not understand the page collection that can be accessed in twig template in this link - https://learn.getgrav.org/content/collections.

I am learning with antimatter theme. I created a listing page using blog.md and made the collection in the blog.md frontmatter. But, in the section accessing collections in twig it says : Grav creates a collection page.collection that you can access in a twig template with:

{% for p in page.collection %}
\<h2>{{ p.title }}\</h2>
{{ p.summary }}\
{% endfor %}

In which file is this code contained in? in the blog.html.twig ?

Thanks for replying. I got it. I guess I will have to look up the documentation of twig so that I can stop asking these silly questions.

Not stupid, it's easy to misread the docs when you have pre-existing ideas :)