My JavaScript files don't seem like it is linked to my PHP file.

I am building a WordPress website. I have header.php and calling this header.php file by including

 in my main.php file. I added JS path in the head tag in header.php, but it doesn't seem like it's working(the JS files I added are for a carousel, but does not change anything). I just started learning so I can't even guess what I am doing wrong here. What can I do to link my JS files?
* header.php, main.php, and js folder are in the root folder. Javascript files are in the js folder.

-- This is how I linked JS file in header.php. inside of the head tag

```
<head>
    <meta charset="<?php bloginfo( 'charset' ); ?>" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <script type="text/javascript" src="js/Jquery.js"></script>
    <script type="text/javascript" src="js/lightslider.js"></script>
    <?php wp_head(); ?>
</head>

```