Creating and linking to custom pages in theme

Dear all!

I am wondering if you can help me regarding a wordpress question, regarding this particular theme: https://www.flyerzone.co.uk/freewptheme/

I have noticed that the menu of this demo, links to what it seems like custom pages, i.e pages that were not created in the wordpress dashboard, but as seperate template files.

I know this because when I create pages (in the same theme), the pages in the menu
(created in the dashboard) have unique names, and that the pages all follow the same template:
https://arearugshop.ca/test/test/

It also seems that the menu in the demo might be custom made (or not).

So my question is twofold:
How can I create custom pages?
&
Link to them in the menu?

You may be wondering why I am not asking the creator of the theme, but its rather difficult getting ahold of them, and its a free theme too so they are not obliged to answer.

I hope we can get to the bottom of this.

Cheers,
KB