Can't route in fresh laravel 5.6 installation

Today I started a fresh laravel installation through composer with this piece of code(just as always):

composer create-project --prefer-dist laravel/laravel new_proj

after the installation the welcome page starts successfully with the laravel logo at the center. The problem is I can't route a new url for example when I type the following code the route\web.php, I get the error "Sorry, the page you are looking for could not be found"

Route::get('foo', function () {
    return 'Hello World';
});

another problem is that when I turn on the debug mode in the config\app.php I still get no detailed error to fix the problem.

for possible answers I should say using port:8000 hasn't fix my problem and by the way ... php artisan serve doesn't work too and get this error : Failed to listen on 127.0.0.1:8000 (reason: An attempt was made to access a socket in a way forbidden by its access permissions. .... note that I have checked whether if another service is using this port only to find that no service is using it

I have always used this routine to install laravel and it worked perfectly but with the new version (5.6) it seems that it doesn't work or I am doing sth wrong.

any idea how to fix this ?

via Chebli Mohamed