To start using Vue.js, make sure you have the script file included in your HTML. For example, add the following to your HTML.
<script src="https://npmcdn.com/vue/dist/vue.js"></script>
<div id="app">
{{ message }}
</div>
new Vue({
el: '#app',
data: {
message: 'Hello Vue.js!'
}
})
See a live demo of this example.
You might also want to check out the "Hello World" example made by Vue.js.