You will spend time useful and interesting with Gems.
Determine which one of you move first, and then, one by one start taking gems from the pile. Whoever picks up the last gem loses. It seems very simple, but trust us, it's not.
If you win, you up to the next level, where it will be harder to win. Lost, You go back to the previous level. So, try to reach the top fifth level, where you choose your own rules and you'll keep your status on it even lost. At this level your achievements will be marked with small rubies. The ultimate goal is 5 stars + 5 rubies.