You can right click on the page in modeler >> add widget >> Add-on and select calender widget from there.
And after that, you have to fill in the several data on the tabs of the widget. But first you have to create a entity (tab Datasource) with at the attributes as listed in the tab Attributes.
Then you need to create some MF's to handle the new/onclick/onchange events (tab Bahavior). A Only a commit event will do the trick for the onchange event.
Try it, if you have any questions then post them.
There are some issues with this widget though, I will post a question on the forum also for that.