index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <div>
        <h2>add text</h2>
        <input type="text" id="myInput">
        <button onclick="add()">abb</button>

    </div>

    <ul id="myUL">
        <li>One</li>
    </ul>


<script>
    function add()
    { 

        var li = document.createElement("li");
        var ins = document.getElementById("myInput").value;
        var t = document.createTextNode(ins);
        li.appendChild(t);
        
        document.getElementById("myUL").appendChild(li);
        document.getElementById("myInput").value = "";
    }
    
</script>
</body>
</html>