Go to "content">"design">"configuration">
You see a table which shows the websites, stores and storeviews that have been setup. Probably it;'s best to choose the top option (press 'edit'), which is setting this global for the shop. You now will see: "scope: Global", Default Theme and Design Rule. In that section there is a tab 'HTML Head' click on that and a form appears. You can also set a favicon page title, meta tags and keywords there and somewhere under there is a field called "Scripts and Style Sheets" you can place the Analytics code there. save the configuration and see if it's now working.
that would be something like this code you should add there (this is an example code):
<!-- Google Analytics -->
<script>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
ga('create', 'UA-XXXXX-Y', 'auto');
ga('send', 'pageview');
</script>
<!-- End Google Analytics -->
