Gems are items that will help you acquire pawns and frames of your favorite topics. To get them, you must win games in "Mountain Track"; each time you achieve victory you will receive 5 gems, among other rewards.
You will be able to view your balance of these items in the upper right corner of the main screen, in the pink gem icon.
To exchange them for collectibles you must access the "Inventory" section, selecting the backpack icon in the bottom bar of the screen. There you will see the pawns and frames that you can obtain using your gems