I edited your original note to correct the thread title spelling.
As the others have noted, you will be billed $10 per day per person for tips and this will be the first charge placed on your shipboard account. If you buy tours on the ship, these will also be charged to your account so you don't need to worry about cash for tours purchased in this manner.
The porters at the pier will expect a tip of 1 to 2 dollars per bag and you need to do this both coming and going. Believe me, the porters are worth it on debarkation day.
Personally, for Caribbean cruises we always bring 200 dollars for each port we will visit, so if we stop at three ports then we have $600 set aside for them. This is souvenir, cab, eating, drinking money. I then double this total amount and keep the extra in the safe in our cabin. It has never failed me and we have never run out of cash. It is important to get lots of small bills too. And don't forget to have more than one credit card with you, in case one is lost or stolen.