It worked for me, after I included the related libraries in the html:
<link rel="stylesheet" href="//code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css">
<script src="//code.jquery.com/jquery-1.10.2.js"></script>
<script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
Here is a demo: https://jsfiddle.net/6cht0v0L/
The jquery code:
$(function() {
$( "#selectable-1" ).selectable();
});
Here is the html:
<ol id="selectable-1">
<li class="ui-widget-content">Product 1</li>
<li class="ui-widget-content">Product 2</li>
<li class="ui-widget-content">Product 3</li>
<li class="ui-widget-content">Product 4</li>
<li class="ui-widget-content">Product 5</li>
<li class="ui-widget-content">Product 6</li>
<li class="ui-widget-content">Product 7</li>
</ol>