Where do I see my coin balance?

On the Rewards screen, with balance, history, and redeem options.

GoCoins: Earn & Redeem

On the Rewards screen, which shows your current balance, your past video performance, and your options to redeem.

It is also where you will find refer and earn and any current ways to earn more.

Your onboarding coins carry a status line there too. It reads as active while you are active, and if a quiet stretch starts a countdown, it tells you exactly how many coins are involved and how many days you have to keep them. See how your coins stay active.