If you need something like laravel native helper url() or asset(), etc.

create file helpers.php in the app directory.

in composer.json you need something like:

"autoload": {
        "files": [
            "app/helpers.php"
        ],
        "psr-4": {
            "App\\": "app/"        
        }
    },

in the file write custom helper function:

if (! function_exists('super_helper')) {
    /**
     * My custom super helper
     *
     * @param  array  $array
     * @return array
     */
    function super_helper(array $array)
    {
        return $array;
    }
}

in console run

composer dump-autoload