When you add a Date attribute is added, a new date field appear appears on the Attributes panel.

A Date field accepts all characters, but if you enter a wrong date format, or any character except numbers, borders of the field's border will became become red, to show you an invalid input.

By clicking on the Calendar icon on the right side of the text box of the attribute, a calendar will show, so you can select be displayed, allowing to select a date from the calendar.