When a sale has been voided the transaction is canceled and not processed.
So if you were to have an item scanned at the register but then voided it before the transaction went through then the money would not be taken from your credit card or debit card.
If you brought the merchandise back to the store and requested a refund then the merchandise would be scanned again and then they would issue a refund.
The refund would then be in the form of cash or through your debit or credit card depending on how you paid for the item.
Voiding the transaction just cancels the transaction and a refund is where you get your money back.
However if you bought something online and the money already taken out of your credit or debit card and then you canceled the transaction.
Then the seller would void the transaction and have a refund sent back to you.