Hi, Kathie!
If you pre-ordered your
Disney PhotoPass+ (great discount, isn't it?) then you should receive a voucher in the mail which you will then take to a photo viewing station at one of the Walt Disney World parks or Downtown Disney. A Cast Member will then give you your PhotoPass+ lanyard which can be used for PhotoPass photos throughout the parks as well as select attractions and dining locations. (Since we've chatted about lanyards in your other question, I'll add this tip for you. If you purchase a lanyard that you like in WDW, you can simply remove the PhotoPass+ card from the PhotoPass+ lanyard and tuck the card in with your other items in your new lanyard. The PhotoPass+ lanyard isn't the important part of the package, the card is!)
If you've ordered Disney's PhotoCD, go onto the link above and select "Learn More" under PhotoPass CD. Click "Order Now" and a box will pop up with the option to "Show Terms and Conditions." Click there and you'll find instructions on how to apply the credit you've purchased to your PhotoPass account.
For more information, call a Cast Member at Disney PhotoPass at (407) 560-4300 or email them at disneyphotopass_support@disneyworld.com.
Happy planning! Be sure to keep those questions coming our way, Kathie. We love to help!