Add the <DxCalendar>...</DxCalendar> markup to your application.
A user should click a date to select it. To enable multi selection, set the EnableMultiSelect to true.
To select a range of dates, a user should select the initial date, hold the left mouse button down and move the mouse to the final date. To add/remove individual dates to/from the selection, a user should click a date with the Ctrl key pressed.