Custom Checkout

I have an issue, when I try to customize the checkout button it’s not working, I don’t know exactly how to work this customization system, I read the documentation and create a template, but I don’t know how to continue. What I must to do if I want to the functionality of the button? :

    <div id="snipcart-templates">
            <!-- The template must have a single root element -->
            <div class="root">
                <button>Click here!</button>