@a10703ant
The Date function expects three parameters, the year, the month and the day. So, the formula:
Date(yourYearDropDown.Selected.Value, yourMonthDropDown.Selected.Value, 1)
will produce a date that is the first day of the selected year and month.
For the second datepicker, you wanted the last day of the month. So, the trick is to add 1 month to the first day of the month and then subtract 1 day. That will be the last day of that month.
DateAdd(DateAdd(Date(yourYearDropDown.Selected.Value, yourMonthDropDown.Selected.Value, 1), 1, Months), -1, Days)
So in the above formula, we again get the Year, Month and Day 1 date, and then add 1 month to it and subtract 1 day from it. That's the last day.