$("#button").click(function () {
$('.item').append('<div>new div</div>')
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<div class="main" id="container">
<div class="item">
items
</div>
</div>
<button id="button">
Click me
</button>
hope it will help