When you open your menu in-game (top right), you will see a pop-up that says 50 free dice/connect. If you choose to interact with this button, you will be redirected to log in to your Facebook account. If the login is successful, the pop-up will close, and you will receive your bonus rolls. Another way to connect your Facebook account is to select the more button when you go to attack. This drop-down menu will give you the option to link your Facebook account and receive 50 free dice.