To see the APY, on the Accounts screen, tap Savings > Varo Savings Account, then Details (upper right). You can also find the APY here.
APY is the amount of money you could earn on an account in a year, based on the interest rate and how frequently interest is compounded (meaning interest is added to the principal, so you also earn interest on interest). It helps give you a better idea of what you could earn on an account than looking at the interest rate alone.
You can find the interest rate and APY in the Savings Account Agreement.