menu.hbs partial

The menu partial is used for rendering menus at your website.
This partial should get a param with a structure of the menu to render:

{{> menu menus.mainMenu}}

Above code will render the main menu of the website.

You have not include partials/menu.hbs in your theme. In this case Publii will load the following default menu.hbs file:

{{#unless level}}
<nav>
{{/unless}}
    <ul{{#if level}} class="submenu submenu-level-{{level}}"{{else}} class="menu menu-level-1"{{/if}}>
        {{#each items}}
            <li{{menuItemClasses}}>
            {{#if link}}
            <a href="{{menuUrl}}"{{#if title}} title="{{title}}"{{/if}}{{#if target}} target="{{target}}"{{/if}}{{#if rel}} rel="{{rel}}"{{/if}}>{{label}}</a>
            {{else}}
            <span{{#if title}} title="{{title}}"{{/if}}>{{label}}</span>
            {{/if}}

            {{#if items}}
                {{> menu}}
            {{/if}}
        </li>
        {{/each}}
    </ul>
{{#unless level}}
</nav>
{{/unless}}

Menu positions are defined in the menus section of config.json, and the default partial uses the menuUrl and menuItemClasses helpers.