Datepicker is a useful library wihch can provide user friendly interface just like a real calendar. The tagging method needs to be changed by Bootstrap version

Datepicker combination with Bootstrap 3.3.7

Datepicker works with Bootstrap 3.3.7 as well as any version of jQuery

<!-- bootstrap -->
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" >
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

<!-- jquery -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>

<!-- moment -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.3/moment.min.js" ></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.3/moment-with-locales.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.3/locale/ko.js"></script>

<!-- bootstrap datetimepicker -->
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.47/css/bootstrap-datetimepicker.min.css"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.47/js/bootstrap-datetimepicker.min.js"></script>

<div class="container">
    <div class="row">
        <div class='col-sm-6'>
            <div class="form-group">
                <div class='input-group date' id='datetimepicker1'>
                    <input type='text' class="form-control" />
                    <span class="input-group-addon">
                        <span class="glyphicon glyphicon-calendar"></span>
                    </span>
                </div>
            </div>
        </div>
        <script type="text/javascript">
            $(function () {
                $('#datetimepicker1').datetimepicker();
            });
        </script>
    </div>
</div>

Datepicker combination with Bootstrap 5.1.3

<!-- jquery -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>

<!-- Bootstrap 5.1.3 --->
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css" rel="stylesheet" crossorigin="anonymous">
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/js/bootstrap.bundle.min.js" crossorigin="anonymous"></script>

<!-- Datepicker -->
 <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.47/css/bootstrap-datetimepicker.min.css"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.47/js/bootstrap-datetimepicker.min.js"></script>
 
<div class="input-group date datepicker">
	<input type="text" placeholder="yyyy-mm-dd" class="form-control" name="dd" id="dd"><span class="input-group-addon">
	<i class="glyphicon glyphicon-th"></i></span>
</div>

<script>$('.datepicker').datepicker({format:'yyyy-mm-dd'});</script>