Send value of calendar to a form using the post method

I am such a newbie at this. and the answer will be really obvious to those that know.
I want to send the value of the calendar to a php file using the variable Arrival.

Here is what I have


here is the php file <?php $Arr_Date= strtotime($_POST['calendar']); echo $Arr_Date; echo "
"; ?>

Sorry to be so dumb


you have to add name attr to input:

then using it retrieve value on php end:
$Arr_Date = strtotime($_POST[‘my_calendar’]);

Thx heaps