To be implement Navbar on your page, you need to set a placeholder like that:

<div id="header-placeholder"></div>

and those script

 <script src="/components/navbar/navbar.js" type="module"></script>

This will then place the header inside of the #header-placeholder div.

To implement the Footer on your page, you need to set a placeholder like that:

<div id="footer-placeholder"></div>

and those script

 <script src="/components/footer/footer.js" type="module"></script>

This will then place the footer inside of the #footer-placeholder div.