There used to be both a family and an adult talent show. More recently, this became a family show only.
There will be an announcement in the Navigator about sign ups. They are at the cruise desk. THey are limited to the first people signing up. Each performer has a maximum of 3 minutes. It is purely a show, there is no "contest" as some posters have mis-understood.
The acts I've seen have ranged from 3 year olds "dancing" in circles to some 10+ year olds doing very nice music, dance, etc.
DCL will provide a live pianist if you need an accompanist. You will need to have sheet music or the pianist may have something (especially if you are doing something Disney). In addition, they have ther karoke music available. For dance acts, you can bring your own CD. They provide an electronic keyboard. ANy other instruments or tools needed are your responsibility.
It really isn't a big deal. DD (now 14) is a good pianist (studies at our local University, etc.) She has played several times, but on other cruises she has chosen not too. We saw a good ballerina (about age 12), a juggler, and a stand up comic who were great. In addition, we've seen several adults, some of whom were semi-professional in their non-cruise lives. We've also seen some totally strange things that you wonder why/what they were doing.
It is limited to the first 15 sign ups...again, no ability assessment or anything. It is attended mostly by the families and tablemates of the performers, but is open to anyone. There is a mandatory rehearsal held either the day before or the afternoon of the show--this is also in the Navigator when the sign ups are posted.