The prize board is a section in which you will be able to place your collection cards and get prizes every a certain amount of time. It is located on the main screen, under the pending games section.
You will be able to place up to three cards at the same time to get the free prizes from your cards. If you haven't placed a card yet, you will see three empty spaces and, if you tap on any of them, you will be redirected to a section with all your cards so that you can choose the one you want to place.
If you have already picked a card and you want to replace it, you will have to tap on it and select 'Replace'. There, you will also be redirected to a section with all your cards so that you can pick the one you want to place.
You will also be able to select the cards to be added to the board from your Album. To do so, go to Get more cards>Album and once you are there, select the card you want and tap on 'Add'. If you already completed the board, the game will ask you to select the card you want to replace.
You will see the time you have left to get your prize in each card and, once the timer reaches zero, you will have to tap on the card to claim your prize.