During one week, you might do a lot of different things, such as work, spend money and play. You work for the money that pays for the necessities of life and the things you do for fun in your free time. More than likely you will have at least a checking account to keep your money safe and accessible for all these activities. With the bank safely keeping your money in a checking account, you have the security and the convenience of being able to track your transactions, but it's your responsibility to track them too. If you don't, you risk overdrawing your account and bouncing checks or using a debit card against an account that does not have the funds to back up your transaction. By reviewing your monthly bank statements with your own checkbook, you can reconcile your account and balance a checkbook to avoid these problems.
For more information about how compound interest can make your money grow, check out the U.S. Securities and Exchange Commission website.