using jQuery in a javascript file

using jQuery in a javascript file

So I am just starting jQuery, and I am beyond confused. I am working on a assignment, and I need to put jQuery code in my javascript file. I need to make it so that it doesnt execute until the page has loaded, and add classes to div elements. Do I put the <script src="jquery-3.2.1.min.js"></script> in my javascript file or my html file? Because if I put it in my javascript file, then none of my javascript runs after that tag. So where does that script src go?

Also for waiting for the page to load I got the code $(window).on('load', function() {} so would my javascript code go in those braces? So that code is not executed until the page loads?