Answers for "do i have to include a js file in my html"

include script in html

<script type="text/javascript" src="/path/to/script.js"></script>

how to connect a js file in html

<!--if you save the javascript file in a folder-->
<script type="text/javscript" src="foldername/filename.js"></script>
<!-- If you save the file in the parent folder-->
<script type="text/javscript" src="filename.js"></script>