What is the cancel button supposed to do ?

Hmmm....

If you are talking about Online/Correspondence chess then the cancel button is if you make a move and want to cancel it before you submit the move. It just resets the board the current position.

 I click on the square the piece was at and reset is automatic to current position , so to me the cancellation button sits there looking pretty.

When will this feature be implemented?

check your settings, option for move indicator , coloured track .

Yeah, it does it like that too. Just checked and you can make a move, click the starting square, or any other square, and it resets too. When I have used the feature, I rarely used the Cancel button, though I think I have a time or two.

It is already a feature of for Online/Correspondence style chess. In your Online Chess settings you can change the Move Preferences, Confirmation section to I will click the SUBMIT button to confirm my move.

The other option is for touch move; so if you have that one then as soon as you move a piece the move is done and you can't change it.

Thanks; Martin _ Stahl , I have never used touch move setting , and a simple question has been answered by a simple explanation . CHEERS .