Edit in JSFiddle

    var app = new Vue({
        el: '#app',
        data: {
            fruits: []
        }
    })

              
<!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset='utf-8'>
    <title>Vue App</title>
    <link href="main.css" rel="stylesheet">
</head>
<body>
<div id="app">
  <p>Fruits: {{ fruits }}</p>
  <input type="checkbox" id="orange" value="orange" v-model="fruits">
  <label for="orange">orange</label>
  <input type="checkbox" id="banana" value="banana" v-model="fruits">
  <label for="banana">banana</label>
  <input type="checkbox" id="strawberry" value="strawberry" v-model="fruits">
  <label for="strawberry">strawberry</label>
</div>
<script src="https://cdn.jsdelivr.net/npm/vue@2.5.13/dist/vue.js"></script>
<script></script>
</body>
</html>