If you have trading cards you don't need, then the goal wall is place to go to.
To access the Goal-wall, go to Cards -> Goal wall in the main menu.
Hint!
You need to build the Fair, in order to unlock the Goal wall!
The goal wall is pretty straight-forward, you select the card that you want to try to win and then put in 5 cards for a shot on the wall. Simply drag 5 cards into the card slots on the bottom right and hit the "5 cards" button to shoot.
You can also use a Goal wall coupon to try your luck at the goal wall.
Rarer the cards that you have placed in the slots, the better is scoring chance. The scoring chance applies to both, the main and secondary prizes.
In case you miss the main or the secondary prize, you will then receive a consolation prize (card).
Every day you can use the goal wall up to 10 times.