Writing and editing Jquery on Atom editor

Im fairly new to web development so forgive me if this is a stupid question: Im using Atom (github's text editor) and I want to add a jQuery file to my website. I tried using jQuery with a CDN writing this on my index.html:

<script src="//code.jquery.com/jquery-1.12.0.min.js"></script>
<script src="js/master.js" type="text/javascript" charset="utf-8"></script>

This, however, doesn't seem to work. Any ideas on how to do it? Thanks a bunch!