Arguments to wp_nav_menu() are not working

I installed WP locally today and began coding my own theme. I have pretty much no formal knowledge in PHP. I can do CSS and HTML.

For PHP, I’m using the WP Codex.

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That is my header.php
No matter what container, container_class, container_id I ask wp_nav_menu to use, it doesn’t change a thing. It’s the same for pretty much every argument I think.

Say, I want to use nav as the container. Won’t work. It will always land up in a div with “menu” class.

What is going wrong in here?