Brian, gratuities for non-suite guests are suggested at $11.65 per person, per day. This includes children. That total covers your waiter, assistant waiter, Head Waiter, and room steward.
You can pre-pay the gratuities along with your final payment for your cruise. There are some circumstances under which you are required to pre-pay the gratuities. Since you're with a group, if your group coordinator has requested "round robin" seating at dinner, where your group members are able to sit at any of your group's tables and not necessarily the same table each night, that requires pre-payment. If you choose the flexible dining program where you go to the dining room at a different time each night and sit at a different table, that also requires gratuity pre-payment.
Tips to bar staff at 15% are included on the bill with each drink you order.
If you don't pre-pay the gratuities, you have two options on the ship. You can go to the Guest Relations Desk within the first couple of days onboard, and ask that your tips be put onto your onboard account. Otherwise, you can pay tips in cash on the last full day of your cruise. Your room steward will give you envelopes and a list of suggested tips. You put the tip into the appropriately labeled envelope, and hand each envelope to the appropriate person. To my mind, it's much easier to either pre-pay or add tips to your onboard account.
The amount of the gratuity is a "suggestion" but of course, you're always free to give more money to anyone you think has gone above and beyond. Many people on this board suggest giving some additional cash to your room steward on the first day of the cruise, which, they say, ensures extraordinary service during the cruise.