Cabana's is not available for evening meal on the first and last night of the cruise. It is a seated meal, a server will present you with a menu from which you will order. The menu will be items available in the dining rooms that night with the addition of a steak or two - usually NY Strip and another option. You can go anytime during their service from, I believe, 6:00pm to 8:00pm. You are not able to make a reservation for this service, you just show up. The atmosphere is generally much quieter than the main dining rooms.
The servers there are those who are "in training". We have had good, attentive service when dining there. Others have posted about not so great service. One night the server suggested I try the Truffle pursiettes with my NY Strip...she was spot on, they were absolutely delicious together.