This workflow is based around a holiday request. In order to do this we need a content definition, which defines the structure of the case document which will be used throughout the workflow. It contains two fields, toDate and fromDate.
Both of these fields are defined to be of converter type date and they are both required.
The content definition itself is called HolidayRequest.

In order to create this content definition right-click in a folder in the hierarchy and select Create\Content definition from the context menu.
This will display the content definition dialog as shown below.

In the "Fields" area of the dialog, right click and select "New Field ..." from the context menu. Call this field "toDate". Change the converter type of this field to be "date". Alter the label of the field to "To date".
Repeat for a second field called "fromDate".

Click "OK" to save this definition to the hierarchy.

For more details on how to create a content definition see this "how to".