Depending on the ship with one or 2 flowriders, there is a schedule for boogie board, self assisted stand up and advanced stand up or mixed wave for those with one flowrider.
In order to do stand up, you first must try the boogie board, then you can go to the mixed wave session or self assisted stand up. they give you 2 tries to get your bracelet each session. Once you have you wristband you can go during the relevant sessions. No lessons required.