How to store the date clicked on a calendar as a variable to pass in a query

Dear Listers,
I have to build a screen that tracks despatched goods on trucks on a certain date. I have created a form (using C# and ASP.NET) where I am displaying the calendar and am allowing the user to select the date he wants to check for the despatched goods.
My question is how to store the date that was clicked by a user in a variable which I want to use it later in an SQL query.
Should I store the date as a session variable? Suppose I want to display the date that the user clicked, how do I display it?
Thanks,
Pragya
 
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