How do dates works?

Hello,

Can someone please explain to me how date controls work?

What does the check mark mean and how is it used?

How do I get a date control to be blank until a date is entered on a file card?

How do I set a date to go in a variable as today's date automatically but still stays as today's date tomorrow and a user is not able to change the date later?

How do I set up a date so the user chooses a future date from a calendar and then it always stays as that date and a user is not able to change the date later?

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