<form>
    <table id="table">
        <tr>
            <td><p>form</p></td>
            <td>
                <input type="text" value="" id="vkid" >
                <input type="button" value="Перейти" id="but" onclick="gotovkpage()">
            </td>
        </tr>
    </table>
</form>
<script>
function gotovkpage(){
  var id = document.getElementById("vkid").value
  window.location = "https://vk.com/" + id
}
</script>