It means, "It's your decision to make."

It means : its your turn to choose or do st or make decision.

We use it to mean, 'I will wait for your response/action/etc'. Two friends have a ball and two tennis rackets. They are not playing hard, just hitting it back and forth. One misses, so the second player has to wait for the first player to take the initiative, in this case to start playing again; because the ball is on their side.

If there are two courts, you will be in one and your friend is in the other court. If the ball is in the other court, it is not in your court and in your friends court. The "so to speak" part means it could be in between courts but closer to your friends. I hope that helps.