<script>
$(document).ready(function(){
    $('#getUser').on('click',function(){
        var user_id = $('#user_id').val();
        $.ajax({
            type:'POST',
            url:'test.php',
            dataType: "json",
            data:{user_id:user_id},
            success:function(data){
                if(data.status == 'ok'){
                    $('#userName').text(data.result);

                    $('.user-content').slideDown();
                }else{

                    alert("User not found...");
                }
            }
        });
    });
});

<input type="text" id="user_id" />
<input type="button" id="getUser" value="Get Details"/>
<div class="user-content" style="display: none;">
    <h4>User Details</h4>
    <p>Name: <span id="userName"></span></p>
</div>