Most likely they will scan your parking permit and the charge will go on your room bill. It is $12 which is just the price of the valet parking, then you need to add the tip to the driver(s). If you notice your parking pass will have a barcode on it. We found out the hard way because we got the charge on our room at Pop after eating at Narcoossees, however, will showed them our TiW card and receipt and they "said" it was not charged, but it was and we had the front desk remove it.
The only way the valet parking is free is if you have a TiW card and dining at the restraurants-- as mentioned you will need to show the TiW card and receipt. And DVC members get free valet parking at DVC resorts too. (of course, tip is extra and expected, even if it is free.)