There are three types of currency used in Flick Arena: Gold, Gems, and Fragments.
Gold is used to upgrade Cards when enough pieces have been collected to reach the next level. This can be done by selecting the Card ready for upgrading, and pressing the 'Upgrade' button (the button will show the Gold cost for the upgrade.) Gold is earned as a reward for Matches, spending Fragments, and can be purchased for Gems.
Gems are used to purchase Chests and Gold packs in the in-game Shop. The Gem cost of these items are shown on their Shop icons. Gems are also used in some special events to continue after a loss, rather than starting over. Gems are earned as rewards for Matches, and can be purchased for real-world money in the in-game Shop.
Fragments are used to help other members of a players Guild upgrade their Cards when requested. When a Guild member makes a Card Request, it will appear as a message in the Guild Chat, showing the Card requested and how many Fragments are needed. Pressing the 'Give' button will contribute 10 Fragments to the request. There is a cooldown before Fragments can be given for the same request again. Fragments are earned as a reward for Matches.