The AP you get at TDS is still an exchange voucher but it is now on the new gift-card style system that TDS uses. The voucher needs to be validated in the register for the voucher to be valid although most people still use the term activated even though that is not correct.
At that time you will get two receipts, one for the sale and one with the ticket tracking numbers on it. You bring your validated voucher and both receipts (you really only need one but bring both anyway) to Guest Relations at WDW and they will exchange your voucher for an activated AP whose start date will be the day you make the exchange, not the day you bought the voucher.
It is really very much the same AP/PAP system always used for activation of TDS-sold AP's. The only difference now is on the TDS point-of-sale end. You no longer have to wait for a week or two for the vouchers to come in. You get them instantly now.