Where is the Wordpress menu formed?

Question

PHP

Hello. The first day I work with WP, at the moment the task is to slightly change the menu classes in the template. Now the menu is formed as follows: "hook" is registered in header.php (or whatever it is called correctly)
<? $hsHeader->GetMenu('main_menu','nav'); ?>
As a result, a menu of the following form is formed:

<ul class="nav">
<li id="menu-item-1" class="menu-item">Пункт 1</li>
<li id="menu-item-2" class="menu-item">Пункт 2</li>
<li id="menu-item-3" class="menu-item">Пункт 3</li>
</ul>

Interested in where is the function responsible for displaying the menu (as I understand it, this is the GetMenu function)?

Answer 1

in your theme directory there should be a functions.php file there and look for

Answer 2

And no one said that classes can be added to the "Appearance - Menu" menu items in the admin panel ... If you don't find it there, you need to check the "Screen Settings - CSS Classes" menu