Issue with Target.Address

SOLUTION: Sub had to be named "Worksheet_Change" for this to work.

I'm trying to get excel to auto-fill in multiple sheets when one cell in one sheet is updated. I was planning on using the Target.Address function to do this.
However, I can't for the life of me get this to work. I have the following test code in the sheet's code:

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I have also tried using

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None of which were succesful.
I am working in a Macro Enabled workbook, but excel will never display the message box to me no matter how many times I update B19.
Please let me know of any further information I need to provide, and thank you in advance for any help you can offer.

Dont understand what you want
Target.address = [B19].address
Or
Target.address(0,0) =[B19]

Dont understand what you want
Target.address = [B19].address
Or
Target.address(0,0) =[B19]

I want excel to realize I've updated a cell, and then update other cells with that same information. The code I've appended to this post is just test code to see if I can get the listener to work.
The formats you posted did not work either.