i need to know which file is template html file in my website
i have to paste the code in body section of my homepage
below is tag manager guide
Quick Start Guide
The Google Tag Manager container snippet is a small piece of JavaScript and non-JavaScript code that you paste into your pages. It enables Tag Manager to fire tags by inserting gtm.js into the page (or through the use of an iframe when JavaScript isn't available).
To implement Google Tag Manager, copy the code snippet provided in the Tag Manager interface or from below, replacing both instances of GTM-XXXX with your container ID. Paste this snippet into your website template page so that it appears immediately after the opening <body> tag.
<!-- Google Tag Manager -->
<noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-XXXX"
height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
<script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
'//www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
})(window,document,'script','dataLayer','GTM-XXXX');</script>
<!-- End Google Tag Manager -->
Many tag management operations can be achieved by just doing the basic code installation, but if you'd like to have finer grain control over tag events or data, you may want to use some customization using our asynchronous methods.