CDN
<body>の一番下
<script src=”https://cdnjs.cloudflare.com/ajax/libs/rellax/1.0.0/rellax.min.js”></script>
先ほど読み込んだタグのすぐ下に追記
<script>
var rellax = new Rellax('.js-rellax');
</script>
HTML
<div class="rellax" data-rellax-speed="2"> <!-- 要素の中身 --> </div>
