Hi @ghostdragon,
I think @zuurg wants to confirm with you that if you want to update an existing record or create a new record when you press a button.
If you just want to create a new record to your list, you just need to:
Patch(List,Defaults(List),{Date:DatePicker1.SelectedDate})
Note that I assume that you Date column is a Date only column type, if it is single-line-of-text, you need to format the selected date into text string as beklow:
Patch(List,Defaults(List),{Date:Text(DatePicker1.SelectedDate,"dd/mm/yyyy")})