Jquery and wordpress

I started to create my first wordpress template … and here comes the first problem, of course, it doesn’t load the jquery library >_>… I have read several articles about how to integrate it into wordpress but seems not work.

i’ve created the file header.php and inside i’ve added this code https://pastebin.com/c4s4gc8G

After that i inserted in index.php this <?php get_header(); ?>

what’s wrong ? >_<