Add Script in WordPress functions.php

<?php
function mytheme_register_scripts()
{
    $theme_version = wp_get_theme()->get( 'Version' );
    wp_enqueue_script('script', get_template_directory_uri().'/assets/js/script.js', array(), $theme_version, true);
    wp_enqueue_script('bootstrap-bundle-min',get_template_directory_uri().'/assets/vendor/bootstrap/js/bootstrap.bundle.min.js', 
array(), $theme_version, false);
    wp_enqueue_script('swiper-bundle-min', get_template_directory_uri().'/assets/vendor/swiper/swiper-bundle.min.js', array(), $theme_version, false); 
}
add_action('wp_enqueue_scripts', 'mytheme_register_scripts');
?>

Syntax:

<?php
function function-name()
{
    $theme_version = wp_get_theme()->get( 'Version' );
    wp_enqueue_script('script', get_template_directory_uri().'path of script.js', array(), $theme_version, true);
}
add_action('wp_enqueue_scripts', 'function-name');
?>