How to create a page in Wordpress?

Question

WordPress

In WP, I do not understand how to create a page correctly.
I created a navigation and in the navigation in the URL field (arbitrary link) I specify a link to the file that lies at the root of the topic and I get an error 404 or 500.
I tried to create a page (and specify not an arbitrary link but a page in the menu settings), but did not find where to edit this page.
I found an index.php file in the root of the WP with a connection to the index in the root of the theme, I tried to do the same only with another template, I got an error 500 (server error)

require( dirname( __FILE__ ) . '/wp-blog-header.php' );

Maybe you need to set up links somehow.
Please help or throw a link where you can read how to create a page with your code.

Answer 1

https://developer.wordpress.org/themes/template-fi... look at this paragraph.
In short, for a page created through the admin panel, you can create your own template by naming the file in the theme directory in a certain way.